fix(app, expo): Missing fs/promises import in Node 12

[barthap]

Looks like fs.promises was introduced even in Node 10: https://nodejs.org/dist/latest-v10.x/docs/api/fs.html#fs_fspromises_copyfile_src_dest_flags

Description

Node 12 doesn't have fs/promises import. But according to the docs, the fs.promises was introduced in Node 10.

I prefer the asynchronous approach because of better error handling.

Related issues

Resolves #5584

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

CI tests

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[codecov]

Codecov Report

Merging #5585 (fb92e8c) into master (d4b2015) will decrease coverage by 46.98%.
The diff coverage is n/a.

❗ Current head fb92e8c differs from pull request most recent head b53b077. Consider uploading reports for the commit b53b077 to get more accurate results

@@             Coverage Diff             @@
##           master    #5585       +/-   ##
===========================================
- Coverage   71.17%   24.20%   -46.97%     
===========================================
  Files         106       92       -14     
  Lines        4405     3993      -412     
  Branches      941      941               
===========================================
- Hits         3135      966     -2169     
- Misses       1173     2446     +1273     
- Partials       97      581      +484     

[mikehardy]

I updated the doc link to the v10 reference to match your assertion (which does check out - the v10 version of the link works as well) so yes this does seem to be just a "how we reference the API" issue and this should fix it. Thanks for the quick PR @barthap !