Depend bundler from `=> 1.2.2` to `< 2.0`

rails.gemspec

@@ -26,6 +26,6 @@
   s.add_dependency 'actionmailer',  version
   s.add_dependency 'railties',      version
 
-  s.add_dependency 'bundler',         '~> 1.2.2'
+  s.add_dependency 'bundler',         '>= 1.2.2', '< 2.0'
   s.add_dependency 'sprockets-rails', '~> 2.0.0.rc1'
 end