Experiment versions cause confusion with allow_multiple_experiments='control' #612

Describe the bug
When we reset an experiment from dashboard, starting numbered versions of experiments in data, it makes confusion in User.max_experiments_reached? and considers the current experiment as already taken.

The symptom is that subsequent calls to ab_test will always return control, once the user starts to be excluded from alternative choice by max_experiments_reached.

To Reproduce
Steps to reproduce the behavior:

I wrote an example app that reproduces the error. It's in rails because it was easier to me.

here is the app.

1. Go to home page. You'll see the alternatives returned by multiple calls to ab_test. This time it works as usual;
2. Go to split dashboard and click in reset data, so to start a new version in the experiment
3. Now refreshes the app until the first alternative is choosed as other.
4. In this case, the result you see is oher, control, control showing that, after that first call subsequent ones will always return control

Additional context
I've already debugged it. The problem is in User#max_experiments_reached?. The count in L31 doesn't clean up experiment key, that now has :<version> at the end.

I can submit the PR if you like so.