Don't specify bugfix version for Bundler

Travis doesn't always have the latest and greatest. They are currently
using bundler 1.5.1.

Author: Chris Hunt

github-auth.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ['lib']
 
-  spec.add_development_dependency 'bundler',        '~> 1.5.2'
+  spec.add_development_dependency 'bundler',        '~> 1.5'
   spec.add_development_dependency 'cane',           '~> 2.6.1'
   spec.add_development_dependency 'cane-hashcheck', '~> 1.2.0'
   spec.add_development_dependency 'coveralls',      '~> 0.7.0'