Add schema location to PHPCS configuration

Author: lcobucci

phpcs.xml.dist

@@ -1,5 +1,8 @@
 <?xml version="1.0"?>
-<ruleset>
+<ruleset
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="vendor/squizlabs/php_codesniffer/phpcs.xsd"
+>
     <arg name="basepath" value="." />
     <arg name="extensions" value="php" />
     <arg name="parallel" value="80" />