Add missing JSONKeys constants usage instances.

Author: danielrbrowne

Sources/PusherEvent.swift

@@ -64,7 +64,7 @@ open class PusherEvent: NSObject, NSCopying {
      */
     @nonobjc internal func copy(withEventName eventName: String) -> PusherEvent {
         var jsonObject = self.raw
-        jsonObject["event"] = eventName
+        jsonObject[Constants.JSONKeys.event] = eventName
         return PusherEvent(eventName: eventName, channelName: self.channelName, data: self.data, userId: self.userId, raw: jsonObject)
     }
 

Sources/PusherWebsocketDelegate.swift

@@ -13,7 +13,7 @@ extension PusherConnection: WebSocketDelegate {
         self.delegate?.debugLog?(message: PusherLogger.debug(for: .receivedMessage, context: text))
 
         guard let payload = PusherParser.getPusherEventJSON(from: text),
-            let event = payload["event"] as? String
+            let event = payload[Constants.JSONKeys.event] as? String
         else {
             self.delegate?.debugLog?(message: PusherLogger.debug(for: .unableToHandleIncomingMessage, context: text))
             return