chore(CI): include git config in .travis.yml

The tests that involve performing git commits were failing on Travis CI.
This is due to the lack of git configuration. The solution is to
configure the git user on Travis CI before running the tests.
docs(README.md): add build status badge from Travis CI
Merge pull request #1 from Gazler/fix/travis-ci

chore(CI): include git config in .travis.yml