Removing done 'pre-release' TODO from readme.

I implemented the full pre-release spec from semver.org, but forgot to remove
the TODO from the README. This just removes the line from the README.
Merge pull request #5 from amerine/update-readme

Removing done 'pre-release' TODO from readme.
add bump functions and tests
Bump functions no longer return; fix tests
Merge pull request #6 from KAllan357/bumps

Add functions to "Bump" major, minor, and patch