The changelog checker fails when tags are pushed because tag builds lack TRAVIS_COMMIT_RANGE environment variable.
$ git diff --name-only "$TRAVIS_COMMIT_RANGE" | grep CHANGES\.rst
fatal: ambiguous argument '': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
The changelog checker fails when tags are pushed because tag builds lack
TRAVIS_COMMIT_RANGE
environment variable.