Add ping hook method

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

@@ -41,6 +41,13 @@ public abstract class GHHook extends GHObject {
         return Collections.unmodifiableMap(config);
     }
 
+    /**
+     * @see <a href="https://developer.github.com/v3/repos/hooks/#ping-a-hook">Ping hook</a>
+     */
+    public void ping() throws IOException {
+        new Requester(getRoot()).method("POST").to(getApiRoute() + "/pings");
+    }
+
     /**
      * Deletes this hook.
      */