Fix linting

[davidgoli]

My previous PR to migrate to eslint #514 didn't actually work correctly, and nothing was getting linted. This properly enables linting and reconciles conflicts between eslint and prettier.

[codecov-commenter]

Codecov Report

Merging #518 (9336e4b) into master (f066c4e) will increase coverage by 0.12%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master     #518      +/-   ##
==========================================
+ Coverage   88.61%   88.73%   +0.12%     
==========================================
  Files          30       29       -1     
  Lines        2029     2024       -5     
  Branches      753      754       +1     
==========================================
- Hits         1798     1796       -2     
+ Misses        231      228       -3     

Impacted Files	Coverage Δ
.eslintrc.js	0.00% <ø> (ø)
src/dateutil.ts	96.87% <ø> (ø)
src/index.ts	100.00% <ø> (ø)
src/nlp/index.ts	100.00% <ø> (ø)
src/parsestring.ts	94.89% <ø> (ø)
src/nlp/parsetext.ts	52.92% <73.68%> (-0.17%)	⬇️
src/nlp/totext.ts	94.00% <93.93%> (-0.03%)	⬇️
src/cache.ts	92.98% <100.00%> (ø)
src/datetime.ts	90.00% <100.00%> (ø)
src/helpers.ts	96.36% <100.00%> (ø)
... and 11 more

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