Support ms resolution.

Patch from Jay Dawes <ajaxous@gmail.com>

src/datasource-zabbix/responseHandler.js

@@ -72,7 +72,7 @@ function convertHistoryPoint(point) {
   // Value must be a number for properly work
   return [
     Number(point.value),
-    point.clock * 1000
+    point.clock * 1000 + Math.round(point.ns / 1000000)
   ];
 }