Add missing PSR12 standard to installed standards list

... and remove the PHPCS standard which was removed in PHPCS 3.0.

Author: jrfnl

wiki/Usage.md

@@ -238,7 +238,7 @@ Multiple coding standards can be checked at the same time by passing a list of c
 PHP_CodeSniffer can print you a list of the coding standards that are installed so that you can correctly specify a coding standard to use for testing. You can print this list by specifying the `-i` command line argument.
 
     $ phpcs -i
-    The installed coding standards are MySource, PEAR, PHPCS, PSR1, PSR2, Squiz and Zend
+    The installed coding standards are MySource, PEAR, PSR1, PSR2, PSR12, Squiz and Zend
 
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