Modify for travis

[rvm 2.0.0]
Bundler could not find compatible versions for gem "bundler":
  In Gemfile:
    bundler (~> 1.5.1) ruby
  Current Bundler version:
    bundler (1.3.5)

[rvm 2.1.0]
Bundler could not find compatible versions for gem "bundler":
  In Gemfile:
    bundler (~> 1.5.1) ruby
  Current Bundler version:
    bundler (1.5.0)

rubicure.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "activesupport", "~> 4.0.1"
   spec.add_dependency "hashie", "~> 2.0.5"
 
-  spec.add_development_dependency "bundler", "~> 1.5.1"
+  spec.add_development_dependency "bundler", ">= 1.3.5"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec", "~> 3.0.0.beta1"
   #spec.add_development_dependency "rspec-parameterized"