Use the new build env on Travis

more capacity, more ram, dedicated cpu cores, faster vm start times
Merge pull request #22 from joshk/patch-1

Use the new build env on Travis
Add a Gemfile for Rails 4.2
WIP
fix travis build
Do not build Rails 5 with ruby < 2.1
Fix <attribute>_before_type_cast on Rails 4.2
Avoid `serialized_attributes` deprecation notice
Avoid reset_<attribute>! deprecation notice