Set ChangeTracker default limit to zero

Per commented by @hideki, we should explicitly set the limit to zero which means no limits.

https://github.com/couchbase/couchbase-lite-android/issues/955

Author: pasin

src/main/java/com/couchbase/lite/replicator/ChangeTracker.java

@@ -102,6 +102,7 @@ public ChangeTracker(URL databaseURL, ChangeTrackerMode mode, boolean includeCon
         this.includeConflicts = includeConflicts;
         this.lastSequenceID = lastSequenceID;
         this.client = client;
+        this.limit = 0;
         this.requestHeaders = new HashMap<String, Object>();
         this.heartBeatSeconds = Replication.DEFAULT_HEARTBEAT;
         this.usePOST = true;