Merged in lk-simk/bitbucket-api/add-merge-restrict (pull request #34)

Added 'restrict_merges' restriction to `BranchRestrictions::create()`.

@see https://developer.atlassian.com/bitbucket/api/2/reference/resource/repositories/%7Busername%7D/%7Brepo_slug%7D/branch-restrictions#post

Author: Lukas Kämmerling

lib/Bitbucket/API/Repositories/BranchRestrictions.php

@@ -64,7 +64,7 @@ public function create($account, $repo, $params = array())
 
         $params = array_merge($defaults, $params);
 
-        if (empty($params['kind']) || !in_array($params['kind'], array('push', 'delete', 'force'))) {
+        if (empty($params['kind']) || !in_array($params['kind'], array('push', 'delete', 'force','restrict_merges'))) {
             throw new \InvalidArgumentException('Invalid restriction kind.');
         }