Fix compile error with JSON uint64_t 🚯

Dockerfile

@@ -1 +1 @@
-docker/Dockerfile.alpine
+docker/Dockerfile.ubuntu_artful

ws/IXSentryClient.cpp

@@ -88,7 +88,7 @@ namespace ix
                 ss >> lineno;
 
                 Json::Value frame;
-                frame["lineno"] = lineno;
+                frame["lineno"] = Json::UInt64(lineno);
                 frame["filename"] = fileName;
                 frame["function"] = function;
 

ws/ixcobra/IXCobraMetricsPublisher.cpp

@@ -184,7 +184,7 @@ namespace ix
         msg["data"] = data;
         msg["session"] = _session;
         msg["version"] = kVersion;
-        msg["timestamp"] = getMillisecondsSinceEpoch();
+        msg["timestamp"] = Json::UInt64(getMillisecondsSinceEpoch());
 
         {
             std::lock_guard<std::mutex> lock(_device_mutex);