RVM support

I get this error when I run `:RunSpec` from vim:

```
/Users/lyahdav/.rvm/gems/ruby-2.1.4/gems/bundler-1.10.6/lib/bundler/definition.rb:412:in `validate_ruby!': Your Ruby version is 2.0.0, but your Gemfile specified 2.1.4 (Bundler::RubyVersionMismatch)
```

My default RVM ruby is 2.1.4 (as is the .ruby-version in the directory I start vim from).
My system ruby is 2.0.0 (OS X default).
