Don't prefix /code/ for absolute paths

If a user provides an absolute path to ruleset file, we
won't prepend `/code/`. This behavior seems intuitive and also
prevents breakage with current codeclimate-php configs which may have
come to use `/code` as a workaround.

Author: ABaldwinHunter

Runner.php

@@ -71,7 +71,7 @@ public function prefixCodeDirectory($configRulesets)
         $configRulesets = explode(',', $configRulesets);
 
         foreach ($configRulesets as &$r) {
-            if (!in_array($r, $officialPhpRulesets)) {
+            if (!in_array($r, $officialPhpRulesets) and $r[0] != "/") {
                 $r  = "/code/$r";
             }
         }