fix: sync types with @oclif/parser

[frangio]

This incorporates the changes from oclif/parser#53.

It's a pity that this has to be manually kept in sync. I tried coming up with a way to keep them in sync automatically by reusing the types from the other package but I couldn't think of any solutions that didn't involve big changes. Any ideas?

[codecov]

Codecov Report

Merging #67 into master will increase coverage by 64.55%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #67       +/-   ##
===========================================
+ Coverage       0%   64.55%   +64.55%     
===========================================
  Files           1        5        +4     
  Lines          10      158      +148     
  Branches        2       35       +33     
===========================================
+ Hits            0      102      +102     
- Misses         10       37       +27     
- Partials        0       19       +19

Impacted Files	Coverage Δ
src/flags.ts	55% <ø> (ø)
src/main.ts	61.53% <0%> (ø)
src/util.ts	38.88% <0%> (ø)
src/command.ts	78.75% <0%> (ø)
src/index.ts	35.71% <0%> (+35.71%)	⬆️

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[RasPhilCo]

Thanks! Let's do this for now to fix those types errors and keep thinking on a better way.

[RasPhilCo]

🏄