Fix errors in examples

Changed %d to %lu in printf()

examples/Demo/Demo.ino

@@ -56,6 +56,6 @@ void loop() {
     
     WebSerial.print(F("IP address: "));
     WebSerial.println(WiFi.localIP());
-    WebSerial.printf("Millis=%d\n", millis());
-    WebSerial.printf("Free heap=[%d]\n", ESP.getFreeHeap());
+    WebSerial.printf("Millis=%lu\n", millis());
+    WebSerial.printf("Free heap=[%lu]\n", ESP.getFreeHeap());
 }

examples/Demo_AP/Demo_AP.ino

@@ -53,7 +53,7 @@ void loop() {
     
     WebSerial.print(F("IP address: "));
     WebSerial.println(WiFi.localIP());
-    WebSerial.printf("Millis=%d\n", millis());
-    WebSerial.printf("Free heap=[%d]\n", ESP.getFreeHeap());
+    WebSerial.printf("Millis=%lu\n", millis());
+    WebSerial.printf("Free heap=[%lu]\n", ESP.getFreeHeap());
 
 }