Fix issue for download files in subfolder

After delete this code line, I can download file from subfolder in linux.

lib/providers/filesystem/index.js

@@ -56,7 +56,7 @@ function validateName(name, cb) {
     return false;
   }
   var match = namePattern.exec(name);
-  if (match && match.index === 0 && match[0].length === name.length) {
+  if (match && match.index === 0) {
     return true;
   } else {
     cb && process.nextTick(cb.bind(null,