fix(async): revert back to previous version 'async' module

[linrongbin16]

Fix #257

Regression Test

Platforms

• windows
• macOS
• linux

Hosts

• Test on github.com.
• Test on gitlab.com.
• Test on bitbucket.org.
• Test on codeberg.org.
• Test on git.samba.org.

Functions

• Use GitLink(!) to copy git link (or open in browser).
• Use GitLink(!) blame to copy the /blame link (or open in browser).
• Use GitLink(!) default_branch to open the /main//master link in browser (or open in browser).
• Use GitLink(!) current_branch to open the current branch link in browser (or open in browser).
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.
• Copy git link with 'file' and 'rev' parameters.

[codecov]

Codecov Report

Attention: Patch coverage is 60.76923% with 51 lines in your changes missing coverage. Please review.

Project coverage is 72.89%. Comparing base (df0c4e3) to head (d6e7b38).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
lua/gitlinker/async.lua	59.82%	47 Missing ⚠️
lua/gitlinker.lua	66.66%	2 Missing ⚠️
lua/gitlinker/linker.lua	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #258      +/-   ##
==========================================
- Coverage   73.96%   72.89%   -1.07%     
==========================================
  Files           9       10       +1     
  Lines         845      963     +118     
==========================================
+ Hits          625      702      +77     
- Misses        220      261      +41     

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