Bump "Error Prone" to 2.0.15

and fix a few things :)

smack-extensions/src/main/java/org/jivesoftware/smackx/geoloc/GeoLocationManager.java

@@ -34,6 +34,7 @@ public final class GeoLocationManager extends Manager {
 
     static {
         XMPPConnectionRegistry.addConnectionCreationListener(new ConnectionCreationListener() {
+            @Override
             public void connectionCreated(XMPPConnection connection) {
                 getInstanceFor(connection);
             }