fixes #1461: nyan-reporter now respects Base.useColors, fixed bug in Base.color

Issue #1461.

nyan-reporter now respects `Base.useColors`, because it's now using `Base.color` and `Base.useColors`.

Fixed bug where `Base.color(type, str)` would not return a string when `str` wasn't a string. (so if you tried `stdout.write(Base.color('green', 0))`, you would be doing `stdout.write(0)`, and that throws an error)