findbugs fix

Author: kohsuke

src/main/java/org/kohsuke/github/GHInvitation.java

@@ -10,7 +10,7 @@
  * @see GHRepository#listInvitations()
  */
 @SuppressFBWarnings(value = {"UWF_UNWRITTEN_PUBLIC_OR_PROTECTED_FIELD", "UWF_UNWRITTEN_FIELD",
-    "NP_UNWRITTEN_FIELD"}, justification = "JSON API")
+    "NP_UNWRITTEN_FIELD", "UUF_UNUSED_FIELD"}, justification = "JSON API")
 public class GHInvitation extends GHObject {
     /*package almost final*/ GitHub root;