[Closes #234, Closes #235] Only call package_name thor versions >= 0.18.x
[Closes #232, Closes #233] Clean up gemspec.

- avoid dependency on git
- variable rename to avoid warning
Merge branch 'master' of https://github.com/tmuxinator/tmuxinator

Conflicts:
	tmuxinator.gemspec
Fixed rebase

Conflicts:
	lib/tmuxinator/cli.rb