Enable rubocop-rspec

**This is work-in-progress**

I try to enable `rubocop-rspec` in `rubocop` but keep on getting an error: `Unable to activate rubocop-0.23.0, because parser-2.2.0.pre.1 conflicts with parser (~> 2.1.9) (Gem::LoadError)` - it seams to have something to do with cfc2a31741b0f32d03907d8d9b5169290f7b8f29, but I don't know how to solve it.

Any ideas?