Fixes rake dependency issue between Rails 3.2.13 and Locomotive 2.0.1

Rails (=3.2.13) depends on rake (10.1.0) while locomotive_cms (~> 2.0.1) ruby depends on rake (~> 10.0.0). Rake (~>10.0.0) is equivalent to (>=10.0.0) and (<10.1.0) making the gemspecs incompatible. I changed it to rake (~>10.0) to allow up to rake (<11.0).