Specify rspec version to 2.14.1

It was happening this error because the rspec version was 3.0.1 and "its" was removed from rspec 3

/Users/thiagoborges/projects/jumpup-heroku/spec/jumpup/heroku/configuration_spec.rb:22:in `block (3 levels) in <top (required)>': undefined method `its' for #<Class:0x00000102d17970> (NoMethodError)