Nokogiri 1.6.0 update (temporary)

sax-machine causes compatibility issues. This commit allows feedzirra to run Nokogiri 1.6.0 temporarily by putting the following in Gemfile:
```
gem 'sax-machine', github: 'AutoUncle/sax-machine', branch: 'nokogiri_update', ref: '95e5f8fedb5ed2d1b3b6bdf3e9ac8c3dc5750de7'
gem 'feedzirra', github: 'AutoUncle/feedzirra', branch: 'nokogiri-update', ref: '9b0bd4dd69dc52a9db58dcf51f94107fb9233dad'
```
After a new version of sax-machine is released with this pull request, Gemfile and feedzirra.gemspec should be updated.