Describe your changes

The wasm download can't write the file as the file is opened with READ instead of WRITE.

Issue ticket number and link

Checklist before requesting a review

For each PR

• Add Copyright if it missed:
  - "Copyright (c) 2019-present Axmol Engine contributors (see AUTHORS.md)."

• I have performed a self-review of my code.

  Optional:

  • I have checked readme and add important infos to this PR.
  • I have added/adapted some tests too.

For core/new feature PR

• I have checked readme and add important infos to this PR.
• I have added thorough tests.

Axmol 3.x ------------------------------------------------------------

For each 3.x PR

• Check the '#include "axmol.h"' and replace it with the needed headers.