Disable Travis builds for failing configurations
Disable Travis builds for failing configurations

The Ruby 1.9.3 build consistently fails for Rails 4.x versions.
This is due to a dependency on the `mime-types-data` gem which
is no longer compatible with Ruby < 2.x .

These are two failing Travis  builds for reference:
 - https://travis-ci.org/flyerhzm/bullet/builds/118186461
 - https://travis-ci.org/flyerhzm/bullet/builds/127187543

Therefore, exclude the following configurations:
 - Ruby 1.9.3 and Rails 4.0
 - Ruby 1.9.3 and Rails 4.1
 - Ruby 1.9.3 and Rails 4.2

flyerhzm/bullet,rrosenblum/bullet,PikachuEXE/bullet,flyerhzm/bullet,PikachuEXE/bullet,rrosenblum/bullet,flyerhzm/bullet