Make sure to unset RUBY_AUTO_VERSION

Commit 1204c0642675d82f6132c06f17aa899cb6ecf5e5 made modifications which
renamed RUBY_VERSION_FILE to RUBY_AUTO_VERSION. This make sure we unset
the proper variable.
Change README.md

Emacs seem to be listed twice under Integration. This remove one of them
while preserving the alphabetical order.
Merge pull request #183 from KevinSjoberg/fix-readme

Change README.md
Merge pull request #181 from KevinSjoberg/master

Make sure to unset RUBY_AUTO_VERSION