Change Rails and rspec dependency

[Issue #6] https://github.com/skinnyworm/wechat-rails/issues/6
Fix rspec errors

[Issue #6] https://github.com/skinnyworm/wechat-rails/issues/6
Fix deprecated method of rspec

[Issue #6] https://github.com/skinnyworm/wechat-rails/issues/6
Update dummy application to Rails 4.0

[Issue #6] https://github.com/skinnyworm/wechat-rails/issues/6
Undergrade rspec matcher falsey and truthy

[Issue #6] https://github.com/skinnyworm/wechat-rails/issues/6
Merge pull request #7 from fahchen/master

Add rails4 support