Use whilst instead of forever

this gets rid of the Error object

src/storage/s3.js

@@ -161,29 +161,27 @@ function listDir(apiConfig, dir, batchSize, iteratorCallback, callback) {
             MaxKeys: batchSize
         };
 
-        async.forever(function listAndDownload(foreverCallback) {
-            s3.listObjects(listParams, function (error, listData) {
-                if (error) return foreverCallback(error);
+        let done = false;
 
-                if (listData.Contents.length === 0) return foreverCallback(new Error('Done'));
+        async.whilst(() => !done, function listAndDownload(whilstCallback) {
+            s3.listObjects(listParams, function (error, listData) {
+                if (error) return whilstCallback(error);
+
+                if (listData.Contents.length === 0) { done = true; return whilstCallback(); }
 
                 const entries = listData.Contents.map(function (c) { return { fullPath: c.Key, size: c.Size }; });
 
                 iteratorCallback(entries, function (error) {
-                    if (error) return foreverCallback(error);
+                    if (error) return whilstCallback(error);
 
-                    if (!listData.IsTruncated) return foreverCallback(new Error('Done'));
+                    if (!listData.IsTruncated) { done = true; return whilstCallback(); }
 
                     listParams.Marker = listData.Contents[listData.Contents.length - 1].Key; // NextMarker is returned only with delimiter
 
-                    foreverCallback();
+                    whilstCallback();
                 });
             });
-        }, function (error) {
-            if (error.message === 'Done') return callback(null);
-
-            callback(error);
-        });
+        }, callback);
     });
 }