Use concise arrow function syntax

Author: lukemelia

lib/redis.js

@@ -88,17 +88,13 @@ module.exports = CoreObject.extend({
     if (revisions.length === 0) {
       return;
     }
-    let dataKeys = revisions.map(function(revision) {
-      return `${keyPrefix}:revision-data:${revision}`;
-    });
+    let dataKeys = revisions.map((rev) => `${keyPrefix}:revision-data:${rev}`);
 
     let data = this._client.mget(dataKeys);
     if (!data) {
       return;
     }
-    return data.map(function(d) {
-      return JSON.parse(d);
-    });
+    return data.map((d) => JSON.parse(d));
   },
 
   _listRevisions(keyPrefix) {