fix(pg): use callback when they are provided

Author: gergelyke

lib/instrumentations/pg.js

@@ -26,12 +26,14 @@ function wrapClient (pg, agent) {
       var url = this.database
       var port = this.port
       var args = Array.prototype.slice.apply(arguments)
+      var isCallback = typeof args[args.length - 1] === 'function'
 
       return utils.wrapQuery.call(this, original, args, agent, {
         protocol: consts.PROTOCOLS.POSTGRES,
         url: url,
         host: port ? host + ':' + port : host,
-        method: utils.tryParseSql(args[0])
+        method: utils.tryParseSql(args[0]),
+        disableCallback: !isCallback
       })
     }
   })