Review Bot 3 introduced a new jshint implementation that made use of a
helper file to output as JSON.

Unfortunately, the helper file did not ship with the package, due to the
lack of `include_package_data=True` in the package configuration and
the lack of a `MANIFEST.in` file.

This fixes the packaging, ensuring we now ship the missing file.

Built packages and verified that the helper script, and other files from
our source tree, were in the resulting wheel and source distributions.