[build] Fix env_win.cc compiler errors

Summary: I broke it in D53781.

Test Plan: tried the same code in util/env_posix.cc and it compiled successfully

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D54303

port/win/env_win.cc

@@ -1415,8 +1415,8 @@ class WinEnv : public Env {
     return status;
   }
 
-  virtual Status Env::GetChildrenFileMetadata(
+  virtual Status GetChildrenFileAttributes(
-      const std::string& dir, std::vector<FileMetadata>* result) override {
+      const std::string& dir, std::vector<FileAttributes>* result) override {
     return Status::NotSupported("Not supported in WinEnv");
   }