To solve this problem, instead of using travis default environment, this PR uses a customized Docker image to run the test, just the same way as we do in opprop repository.
Also this PR fix the travis status link in README (Should point to typetools rather than opprop).
The travis failure on master branch might caused by travis internally change on its environment.
(Originally master branch passed travis test:
https://travis-ci.org/typetools/checker-framework-inference/builds/270476972
But then it failed on the same commit later on that day triggered by an upstream commit due to lack of Junit dependencies:
https://travis-ci.org/typetools/checker-framework-inference/builds/270517255)
To solve this problem, instead of using travis default environment, this PR uses a customized Docker image to run the test, just the same way as we do in opprop repository.
Also this PR fix the travis status link in README (Should point to
typetools
rather thanopprop
).