findbugs warning fix

Author: kohsuke

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

@@ -1,12 +1,16 @@
 package org.kohsuke.github;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+
 import java.io.IOException;
 import java.net.URL;
 
 /**
  * @see GitHub#getMyInvitations()
  * @see GHRepository#listInvitations()
  */
+@SuppressFBWarnings(value = {"UWF_UNWRITTEN_PUBLIC_OR_PROTECTED_FIELD", "UWF_UNWRITTEN_FIELD",
+    "NP_UNWRITTEN_FIELD"}, justification = "JSON API")
 public class GHInvitation extends GHObject {
     /*package almost final*/ GitHub root;