Trim trailing whitespace

[jayvdb]

Reasons for making this change:

Trailing whitespace is ugly.

Links to documentation supporting these [rule] changes:

n/a

[shiftkey]

@jayvdb thanks!

[jayvdb]

@shiftkey , any chance we can add some CI to prevent regressions?
I've done the same at https://github.com/dvcs/gitignore/blob/master/.travis/check-whitespace.sh (enhanced at toptal/gitignore#117)

I'd be happy to implement it, ideally using Travis-CI, either raw .sh using git, or in any major scripting language which you prefer, provided it has a wildmatch-like library so that it can grow to check validity of rules and possibly also check inter-relations between rules.

[shiftkey]

@jayvdb I've enabled Travis with an example build that's now passing https://travis-ci.org/github/gitignore/builds/393575258 - feel free to build upon that