Inconsistent naming of the PHPCS ruleset.xml file

[JDGrimes]

In .travis.yml and pre-commit, it is referenced as ruleset.xml. However, the name of the file in the repo, and the symlink created by following the readme's instructions, is phpcs.ruleset.xml. This may be intended, but I don't see any documentation to that effect. (My 2¢: I'd prefer to just make it phpcs.ruleset.xml across the board, if there is no intended difference.)

[westonruter]

@JDGrimes again, thanks!