s3: ensure we list directory

<timestamp>/box_v9.0.0.backupinfo ends up getting listed
when trying to list <timestamp>/box_v9.0.0 !

src/storage/s3.js

@@ -351,7 +351,7 @@ async function listDir(apiConfig, remotePath, batchSize, marker) {
     const fullRemotePath = path.join(apiConfig.prefix, remotePath);
     const listParams = {
         Bucket: apiConfig.bucket,
-        Prefix: fullRemotePath,
+        Prefix: fullRemotePath + '/', // ensure we list contents of the directory and not match other filenames with prefix
         MaxKeys: batchSize
     };
     if (marker) listParams.ContinuationToken = marker;