Make scripts check if PR is targeting `master`

From http://docs.travis-ci.com/user/ci-environment/:

  "TRAVIS_BRANCH: For builds not triggered by a pull request this
   is the name of the branch currently being built; whereas for
   builds triggered by a pull request this is the name of the branch
   targeted by the pull request (in many cases this will be master)."

  "TRAVIS_PULL_REQUEST: The pull request number if the current job is
   a pull request, "false" if it's not a pull request."

So, in order to ensure that the scripts are executed ONLY when the
changes are pushed to the `master` branch, the scripts also need to
check if `TRAVIS_PULL_REQUEST == false`.
Update `CHANGELOG.md`
v0.4.0