Add extra source files in the source tarball

Hi,

It's been quite a while, and I just noticed that I'm two releases behind. ShellCheck is still at 0.3.1 on Hackage, and I was hoping you'd keep uploading releases there.

This patch will add to the source tarball the missing bits I need to let all the heavy lifting to Fedora's Hackage/Cabal tooling. I will update ShellCheck to 0.3.3 for Fedora soon and I hope I'll build the next release directly from Hackage :-)

Cheers,
Dridi