slack CLI flag can be the slack url

[hipstersmoothie]

What Changed

--slack can be:

• a string (this already worked)
• a boolean - when boolean auto will look in the auto.config for a string (this didn't work, args.slack would have overridden config.slack)

Why

closes #23

Todo:

• Add tests
• Add docs
• Add SemVer label

[codecov]

Codecov Report

Merging #103 into master will decrease coverage by 0.07%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage      75%   74.92%   -0.08%     
==========================================
  Files          13       13              
  Lines         940      941       +1     
  Branches      137      138       +1     
==========================================
  Hits          705      705              
  Misses        208      208              
- Partials       27       28       +1

Impacted Files	Coverage Δ
src/cli/args.ts	91.25% <ø> (ø)	⬆️
src/main.ts	23.55% <50%> (-0.12%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #103 into master will decrease coverage by 0.07%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage      75%   74.92%   -0.08%     
==========================================
  Files          13       13              
  Lines         940      941       +1     
  Branches      137      138       +1     
==========================================
  Hits          705      705              
  Misses        208      208              
- Partials       27       28       +1

Impacted Files	Coverage Δ
src/cli/args.ts	91.25% <ø> (ø)	⬆️
src/main.ts	23.55% <50%> (-0.12%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a6cabf3...f68e810. Read the comment docs.