ndb_mongodb: Fix typos in module documentation

src/modules/ndb_mongodb/doc/ndb_mongodb_admin.xml

@@ -272,7 +272,7 @@ if(mongodb_find_one("mgs1", "kamailio", "subscriber", "{ \"username\" : \"111\"
 	</title>
 	<para>
 		Moves to next document in a MongoDB reply. This function can be used
-		after a succesful mongodb_cmd() or mongodb_find(). It returns true if
+		after a successful mongodb_cmd() or mongodb_find(). It returns true if
 		there is a shift to document. The current document becomes available
 		via $mongodb(key) variable.
 	</para>