feat: able to use a custom resolver

[mastilver]

closes #13

[codecov-io]

Codecov Report

Merging #26 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #26      +/-   ##
==========================================
+ Coverage   98.75%   98.82%   +0.07%     
==========================================
  Files           1        2       +1     
  Lines          80       85       +5     
==========================================
+ Hits           79       84       +5     
  Misses          1        1

Impacted Files	Coverage Δ
src/index.js	98.76% <100%> (+0.01%)	⬆️
src/get-resolver.js	100% <100%> (ø)

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