Oldest compatible matplotlib version? #114

import proplot as plot
import numpy as np
with plot.rc.context(abc=True):
    f, axs = plot.subplots(ncols=2, share=0)

# Colorbars
ax = axs[0]
state = np.random.RandomState(51423)
m = ax.heatmap(state.rand(10, 10), colorbar='t', cmap='dusk')
ax.colorbar(m, loc='r')
ax.colorbar(m, loc='ll', label='colorbar label')
ax.format(title='Axes colorbars', suptitle='Axes colorbars and legends demo')

# Legends
ax = axs[1]
ax.format(title='Axes legends', titlepad='0em')
hs = ax.plot(
    (state.rand(10, 5) - 0.5).cumsum(axis=0), linewidth=3,
    cycle='sharp', legend='t',
    labels=list('abcde'), legend_kw={'ncols': 5, 'frame': False}
)
ax.legend(hs, loc='r', ncols=1, frame=False)
ax.legend(hs, loc='ll', label='legend label')
axs.format(xlabel='xlabel', ylabel='ylabel')

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-19-837a2de5d36a> in <module>
      7 ax = axs[0]
      8 state = np.random.RandomState(51423)
----> 9 m = ax.heatmap(state.rand(10, 10), colorbar='t', cmap='dusk')
     10 ax.colorbar(m, loc='r')
     11 ax.colorbar(m, loc='ll', label='colorbar label')

~/anaconda3/lib/python3.7/site-packages/proplot/axes.py in heatmap(self, *args, **kwargs)
   1208         that is suitable for heatmaps: no gridlines, no minor ticks, and major
   1209         ticks at the center of each grid box."""
-> 1210         obj = self.pcolormesh(*args, **kwargs)
   1211         xlocator, ylocator = None, None
   1212         if hasattr(obj, '_coordinates'):

~/anaconda3/lib/python3.7/site-packages/proplot/wrappers.py in _wrapper(self, *args, **kwargs)
   2960         @functools.wraps(func)
   2961         def _wrapper(self, *args, **kwargs):
-> 2962             return driver(self, func, *args, **kwargs)
   2963         name = func.__name__
   2964         if name not in proplot_methods:

~/anaconda3/lib/python3.7/site-packages/proplot/wrappers.py in standardize_2d(self, func, order, globe, *args, **kwargs)
    650     colorbar_kw = kwargs.pop('colorbar_kw', None) or {}
    651     colorbar_kw.setdefault('label', colorbar_label)
--> 652     return func(self, x, y, *Zs, colorbar_kw=colorbar_kw, **kwargs)
    653 
    654 

~/anaconda3/lib/python3.7/site-packages/proplot/wrappers.py in _wrapper(self, *args, **kwargs)
   2960         @functools.wraps(func)
   2961         def _wrapper(self, *args, **kwargs):
-> 2962             return driver(self, func, *args, **kwargs)
   2963         name = func.__name__
   2964         if name not in proplot_methods:

~/anaconda3/lib/python3.7/site-packages/proplot/wrappers.py in cmap_changer(self, func, cmap, cmap_kw, extend, norm, norm_kw, N, levels, values, centers, vmin, vmax, locator, symmetric, locator_kw, edgefix, labels, labels_kw, fmt, precision, colorbar, colorbar_kw, panel_kw, lw, linewidth, linewidths, ls, linestyle, linestyles, color, colors, edgecolor, edgecolors, *args, **kwargs)
   2128         if loc != 'fill':
   2129             colorbar_kw.setdefault('loc', loc)
-> 2130         self.colorbar(obj, **colorbar_kw)
   2131     return obj
   2132 

~/anaconda3/lib/python3.7/site-packages/proplot/axes.py in colorbar(self, loc, pad, length, width, space, frame, frameon, alpha, linewidth, edgecolor, facecolor, *args, **kwargs)
    944         # Generate panel
    945         if loc in ('left', 'right', 'top', 'bottom'):
--> 946             ax = self.panel_axes(loc, width=width, space=space, filled=True)
    947             return ax.colorbar(loc='_fill', *args, length=length, **kwargs)
    948 

~/anaconda3/lib/python3.7/site-packages/proplot/axes.py in panel_axes(self, side, **kwargs)
   1370             The panel axes.
   1371         """
-> 1372         return self.figure._add_axes_panel(self, side, **kwargs)
   1373 
   1374     @_standardize_1d

~/anaconda3/lib/python3.7/site-packages/proplot/utils.py in decorator(*args, **kwargs)
     61         if BENCHMARK:
     62             t = time.perf_counter()
---> 63         res = func(*args, **kwargs)
     64         if BENCHMARK:
     65             decorator.time += (time.perf_counter() - t)

~/anaconda3/lib/python3.7/site-packages/proplot/subplots.py in _add_axes_panel(self, ax, side, filled, **kwargs)
    858         gridspec_prev = self._gridspec_main
    859         gridspec = self._insert_row_column(
--> 860             side, iratio, width, space, space_orig, figure=False)
    861         if gridspec is not gridspec_prev:
    862             if s == 't':

~/anaconda3/lib/python3.7/site-packages/proplot/subplots.py in _insert_row_column(self, side, idx, ratio, space, space_orig, figure)
   1339             # May seem inefficient but it literally just assigns a hidden,
   1340             # attribute, and the creation time for subpltospecs is tiny
-> 1341             axs = [iax for ax in self._iter_axes()
   1342                    for iax in (ax, *ax.child_axes)]
   1343             for ax in axs:

~/anaconda3/lib/python3.7/site-packages/proplot/subplots.py in <listcomp>(.0)
   1340             # attribute, and the creation time for subpltospecs is tiny
   1341             axs = [iax for ax in self._iter_axes()
-> 1342                    for iax in (ax, *ax.child_axes)]
   1343             for ax in axs:
   1344                 # Get old index

AttributeError: 'XYAxesSubplot' object has no attribute 'child_axes'