Travis: minor tweak

Run the integration test with an open ended `testVersion`.

Author: jrfnl

.travis.yml

@@ -41,7 +41,7 @@ script:
     fi
 
   # Test the ruleset.
-  - vendor/bin/phpcs ./Test/WPTest.php --standard=PHPCompatibilityWP --runtime-set testVersion 5.2
+  - vendor/bin/phpcs ./Test/WPTest.php --standard=PHPCompatibilityWP --runtime-set testVersion 5.2-
 
   # Validate the composer.json file.
   # @link https://getcomposer.org/doc/03-cli.md#validate