Search slightly more liberally for git remotes.

I use heroku_plus and I don't want to have to type --app after everything.
The restrictive regex used to detect the current heroku app means that
anytime you change it -- e.g. to add different git hosts in ~/.ssh/config --
--app no longer is autodetected.

Instead, I simply edited the regex a bit to detect (or not; it obviously doesn't
break anything) items like the following:

[remote "heroku"]
  url = git@heroku.com.personal:<my app name>.git

This way, entries in .ssh/config can read something like this:

Host heroku.com.personal
  HostName heroku.com
  ...

That, of course, allows using multiple accounts in an unobstrusive way.
The heroku_plus gem could be edited to adopt that convention and boom, there you go.
Merge pull request #643 from colinyoung/master

Search more liberally for git host/app name to accomodate heroku_plus and other Heroku account switchers