minor #1724 Update groups.md (Orppa)

This PR was submitted for the master branch but it was merged into the 1.3.x branch instead (closes #1724).

Discussion
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Update groups.md

Commits
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8983c9d Update groups.md

Author: stof

Resources/doc/groups.md

@@ -108,7 +108,7 @@ class Group extends BaseGroup
 namespace MyProject\MyBundle\Document;
 
 use FOS\UserBundle\Document\Group as BaseGroup;
-use Doctrine\ODM\CouchDB\Mapping as MongoDB;
+use Doctrine\ODM\CouchDB\Mapping as CouchDB;
 
 /**
  * @CouchDB\Document