NTPClient: Added packetFlush to update() as well. This should hopefully fix those random time delay bugs.

src/NTPClient.cpp

@@ -133,6 +133,8 @@ bool NTPClient::update() {
       this->begin();
     }
 
+    while(this->_udp->parsePacket() != 0) this->_udp->flush();
+
     this->sendNTPPacket();
   }