Run specs with guard-rspec

[ohrite]

• Ignore the tmp/ directory created by running guard-rspec
• Add .ruby-version and .ruby-gemset to gitignore for rbenv

[zachmargolis]

This seems like developer settings to me? I don't use guard-rspec, what is the purpose of commiting these?

[ameuret]

Even if slightly I think it lowers the barrier to entry to would-be contributors and it promotes the use of the spec.

[zachmargolis]

LGTM