feat: 📦 Support ESLint 8

[idahogurl]

Closes #427
Closes #428

What:
BREAKING CHANGE:
Requires ESLint 8. ESLint 8 API changes caused the format function to now be asynchronous.
Requires minimum Node 12 as required by ESLint 8

[codecov-commenter]

Codecov Report

Merging #431 (071b7fc) into master (afc22f5) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 071b7fc differs from pull request most recent head 54aa823. Consider uploading reports for the commit 54aa823 to get more accurate results

@@            Coverage Diff            @@
##            master      #431   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          158       157    -1     
  Branches        23        23           
=========================================
- Hits           158       157    -1     

Impacted Files	Coverage Δ
src/format-files.js	100.00% <100.00%> (ø)
src/messages.js	100.00% <100.00%> (ø)

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[kylemh]

looks good to me! love the energy

[zimme]

LGTM, with 1 comment.

The configuration part might need proper testing to make sure eslint config file merging works properly, etc.

This new overrideConfigFile option seems like it will use the provided config file only and not do any kind of merging with parent config files, etc.

[idahogurl]

@zimme Good catch! Further testing does need to be done. I just need to either add a test or test it on my own with a sample project.

[idahogurl]

Blocked by prettier/prettier-eslint#745 to get the overrideConfigFile option to work.

[chrisbobbe]

Thank you! For the record, this PR fixes

• Stop using ESLint 5's ConfigFile.load, which is gone in ESLint 6. #303
• Support prettier-eslint, prettier, and eslint later than v9.0.2, v1.19.1, and v5.16.0. #304

Is that right?

[idahogurl]

@chrisbobbe Good catch!
Closes #303
Closes #304

[kylemh]

what a machine 🎉