Update useragent filter for new user_agent_parser

The 2.0.0 release of user_agent_parser changed the constructor
syntax slightly. It's also been release to rubygems.org now.
Merge pull request #369 from wotifgroup/gem-release

Update useragent filter for new user_agent_parser
- enable user_agent_parser stuff now that 2.0.0 is released
- style