Highlighting of certain functions is broken #16

CREATE INDEX CONCURRENTLY IF NOT EXISTS albums_title_index
ON albums USING gin (title gin_trgm_ops);

In this example, the in of gin on the second line is highlighted as a keyword.

This is due to this line I think: https://github.com/exu/pgsql.vim/blob/master/syntax/pgsql.vim#L351 — checking for word boundary might be a way to fix it, I'm not sure.