Fixed exponential in timestamp

Author: jonalmeida

src/main/java/com/snowplowanalytics/snowplow/tracker/Tracker.java

@@ -63,7 +63,7 @@ private Payload completePayload(Payload payload, Map context, double timestamp)
         payload.add(Parameter.TRACKER_VERSION, Version.VERSION);
 
         // If timestamp is set to 0, generate one
-        payload.add(Parameter.TIMESTAMP, (timestamp == 0 ? Long.toString(Util.getTimestamp()) : timestamp));
+        payload.add(Parameter.TIMESTAMP, (timestamp == 0 ? Util.getTimestamp() : timestamp));
 
         // Encodes context data
         if (context != null) {

src/main/java/com/snowplowanalytics/snowplow/tracker/Util.java

@@ -51,8 +51,8 @@ public static int getTransactionId() {
         return r.nextInt(999999-100000+1) + 100000;
     }
 
-    public static Long getTimestamp() {
-        return System.currentTimeMillis();
+    public static String getTimestamp() {
+        return Long.toString(System.currentTimeMillis());
     }