Make mUpdateInterval uint32_t for better compatibity with differnet

hardware.

AS decribed in aharshac#5

On some boards (e.g. ATmega like Uno) "int" is only 2 bytes and thus is capped unsigned at only roughly 65000. As mUpdateInterval holds milliseconds this more or less means that you can have 1 minute max as update interval.

src/EasyNTPClient.h

@@ -26,15 +26,15 @@ class EasyNTPClient
     int getTimeOffset();
     void setTimeOffset(int offset);
     unsigned long getUnixTime();
-    
+
   private:
     UDP *mUdp;
     const char* mServerPool = "pool.ntp.org";
     int mOffset = 0;
-    unsigned int mUpdateInterval = 60000;
+    uint32_t mUpdateInterval = 60000;
     unsigned long mLastUpdate = 0;
     long mServerTime = 0;
     unsigned long getServerTime();
 };
 
-#endif
+#endif