feat: support exotic manifests

[zkochan]

pnpm v3.3.0 will support package.json5 and package.yaml (pnpm v3.3.0-0 is already out with the support).

This implementation involves a pnpm library that only supports Node.js>=8.15, so I understand if it will be rejected. Also, a test is required. Just want to know if you'd be fine supporting it. If no, I will publish a fork for pnpm usage.

[codecov]

Codecov Report

Merging #169 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
- Coverage   92.94%   92.93%   -0.02%     
==========================================
  Files          22       22              
  Lines         468      467       -1     
==========================================
- Hits          435      434       -1     
  Misses         33       33

Impacted Files	Coverage Δ
lib/read-package-json.js	100% <100%> (ø)	⬆️

---

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 5017a88...8cc806c. Read the comment docs.

[codecov]

Codecov Report

Merging #169 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
- Coverage   92.94%   92.93%   -0.02%     
==========================================
  Files          22       22              
  Lines         468      467       -1     
==========================================
- Hits          435      434       -1     
  Misses         33       33

Impacted Files	Coverage Δ
lib/read-package-json.js	100% <100%> (ø)	⬆️

---

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 5017a88...8cc806c. Read the comment docs.

[devinrhode2]

HOT DAMN! PNPM HAS BEEN SUPPORTING package.json5 THIS WHOLE TIME???
"Where have I been living" -patrick star

[ghost]

@zkochan @aleee1333 @mysticatea whats the status of this ? Is this going in, or is there a fork already ?