add .travis.yml to suppress Travis-CI testing on master

- Need a .travis.yml file in every branch
- only enable testing for dmd-1.x
- http://docs.travis-ci.com/user/build-configuration/#White--or-blacklisting-branches
Merge pull request #3129 from MartinNowak/disableTravis

add .travis.yml to suppress Travis-CI testing on master