This commit renames PHPCS configutarion file to `phpcs.xml`. With the default name, it is not necessary to use the argument `--standard=phpcs.ruleset.xml` anymore when calling `phpcs`.
PR #17680 added a new PHP 7.1 Travis build job to generate code coverage report. PHPCS was configured to run on all PHP 7.1 build jobs. So this means that after #17680 was merged, Travis started running PHPCS twice.
This commit fixes this issue by setting a new environment variable called `$RUN_PHPCS` and using this variable, instead of the PHP version, to decide when to run PHPCS.
Rodrigo Primo
Claudio Sanches