migrate jshint to eslint

[ChristianMurphy]

configuration migration automated using https://github.com/brenolf/polyjuice.
find and replace used to switch jshint ignore comments for eslint disable comments.

alternative to #1338

---

there are a few unused vars and uses of proto, which jshint missed that eslint catches, that are being flagged.

nodegit/lib/nodegit.js
  1081:1  error  The '__proto__' property is deprecated  no-proto

nodegit/lib/repository.js
  1466:20  error  'promiseChain' is assigned a value but never used  no-unused-vars

nodegit/test/tests/commit.js
  1045:5  error  'signature' is assigned a value but never used  no-unused-vars

nodegit/test/tests/merge.js
   179:11  error  'ourBranch' is assigned a value but never used    no-unused-vars
   213:9   error  'theirCommit' is assigned a value but never used  no-unused-vars
   295:11  error  'ourBranch' is assigned a value but never used    no-unused-vars
   329:9   error  'theirCommit' is assigned a value but never used  no-unused-vars
   454:9   error  'ourCommit' is assigned a value but never used    no-unused-vars
   485:9   error  'theirCommit' is assigned a value but never used  no-unused-vars
   604:11  error  'ourCommit' is assigned a value but never used    no-unused-vars
   635:11  error  'theirCommit' is assigned a value but never used  no-unused-vars
   763:11  error  'ourCommit' is assigned a value but never used    no-unused-vars
   794:11  error  'theirCommit' is assigned a value but never used  no-unused-vars
   881:11  error  'ourBranch' is assigned a value but never used    no-unused-vars
   915:9   error  'theirCommit' is assigned a value but never used  no-unused-vars
  1037:9   error  'ourCommit' is assigned a value but never used    no-unused-vars
  1068:9   error  'theirCommit' is assigned a value but never used  no-unused-vars
  1184:9   error  'ourCommit' is assigned a value but never used    no-unused-vars
  1215:9   error  'theirCommit' is assigned a value but never used  no-unused-vars

nodegit/test/tests/revwalk.js
  114:11  error  'storedCommits' is assigned a value but never used  no-unused-vars

nodegit/test/tests/signature.js
  103:5  error  'time' is assigned a value but never used  no-unused-vars

nodegit/test/tests/stash.js
  157:11  error  'oldContent' is assigned a value but never used  no-unused-vars
  189:11  error  'oldContent' is assigned a value but never used  no-unused-vars

✖ 23 problems (23 errors, 0 warnings)

these could either be ignored or the tests refactored to use the variable.

[implausible]

I actually have a preference for how to go about this one. I was working on bringing this into the library here:
https://github.com/implausible/nodegit/tree/convert-to-es6. Need to rebase that on top of master and address any of the major changes.

[ChristianMurphy]

Thanks @implausible!
That makes sense, I'll take a look into that, from a cursory look, it seems like a bigger lift than I have cylces for at the moment.
Either way, I'll clear this PR since it isn't the desired approach.