update periodic source refreshment to work with the new synchronous SnowlFeed::refresh method

--HG--
extra : rebase_source : 856de0e60d914db302f7b0f0328c1a624ef643b3

modules/service.js

@@ -284,14 +284,11 @@ let SnowlService = {
     let refreshTime = new Date();
     for each (let source in allSources) {
       this._log.info("refreshing source " + source.name);
-      source.refresh(refreshTime, this.onRefresh, this);
+      source.refresh(refreshTime);
+      source.persist();
     }
   },
 
-  onRefresh: function(source) {
-    source.persist();
-  },
-
   /**
    * Determine whether or not an author has at least one message in the database.
    *