Fix REST example for removing included groups from a group

Change-Id: I8047fa702c12150232ebf62bcd16a27eb638c5e8
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/rest-api-groups.txt b/Documentation/rest-api-groups.txt
index 0779579..e3559a3 100644
--- a/Documentation/rest-api-groups.txt
+++ b/Documentation/rest-api-groups.txt
@@ -1090,7 +1090,7 @@
   Content-Type: application/json;charset=UTF-8
 
   {
-    "members": [
+    "groups": [
       "MyGroup",
       "MyOtherGroup"
     ]