use currentTimeMillis() for time

Everybody else does....

xwords4/android/app/src/main/java/org/eehouse/android/xw4/Utils.java

@@ -443,7 +443,7 @@ public class Utils {
     {
         // Note: an int is big enough for *seconds* (not milliseconds) since 1970
         // until 2038
-        long millis = new Date().getTime();
+        long millis = System.currentTimeMillis();
         int result = (int)(millis / 1000);
         return result;
     }