Stop colorizing colorized diffs
Correctly colorize diffs

We have to reset lines that we want to not be red, as this shows as part
of a failed example.
Make DiffPresenter end all hash entries with comma

This fixes a bug where identical entries would show up as an added and a
subtracted line (that differed in the trailing comma) if they were the
last entry in one hash but not the other.
Simplify `DiffPresenter#object_to_string`
Merge pull request #407 from jarednorman/diff-presenter-fixes

Diff presenter fixes