src: fix readability/constructors cpplint warnings

PR-URL: #7462 Reviewed-By: Trevor Norris <[email protected]>

Author: bnoordhuis

src/node_file.cc

@@ -251,10 +251,13 @@ static void After(uv_fs_t *req){
 
 // This struct is only used on sync fs calls.
 // For async calls FSReqWrap is used.
-structfs_req_wrap{
+classfs_req_wrap{
+public:
 fs_req_wrap(){}
 ~fs_req_wrap(){uv_fs_req_cleanup(&req)}
 uv_fs_t req;
+
+private:
 DISALLOW_COPY_AND_ASSIGN(fs_req_wrap);
 };