Use unsigned long for millis

Fixes #133

Author: marcelstoer

src/TimeClient.h

@@ -33,7 +33,7 @@ class TimeClient {
   private:
     float myUtcOffset = 0;
     long localEpoc = 0;
-    long localMillisAtUpdate;
+    unsigned long localMillisAtUpdate;
 
     const char* ntpServerName = "time.nist.gov";
     unsigned int localPort = 2390;

src/WorldClockClient.h

@@ -33,8 +33,8 @@ See more at http://blog.squix.ch
 
 class WorldClockClient: public JsonListener {
   private:
-    long millisOfDayAtUpdate = 0;
-    long localMillisAtUpdate;
+    unsigned long millisOfDayAtUpdate = 0;
+    unsigned long localMillisAtUpdate;
     boolean isHeader = true;
     String currentKey = "";
     String myLanguage;