Fix travis build failure with ruby-head (#132)
Fix travis build failure with ruby-head (#132)

The rubygems upgrade seems to lead to a prompt like this that waits for
user input, eventually timing out and failing the build:

```
bundler's executable "bundle" conflicts with /home/travis/.rvm/rubies/ruby-head/bin/bundle
Overwrite the executable? [yN]
```

Fix by removing the rubygems upgrade.
mattbrictson/airbrussh,mattbrictson/airbrussh