Update to new rubocop version

offence has been renamed to offense
Split `UnitSpecNaming` into seperated cops
Add RSpecDescription cop
Fix rubocop configuration
fix travis config
Fix RSpecFileName cop for non-class specs
Adapt RSpecFileName to commen naming convention
Add RSpecMultipleDescribes cop
Rename cops
Add `RSpecDescribedClass` cop
Add RSpecInstanceVariable cop
Minor cleanup
Merge pull request #3 from geniou/refactoring

Refactoring + new cops