fix: compile for es2020 instead of es2021

[vladfrangu]

Allows users of nodejs 14+ to use shapeshift

[codecov-commenter]

Codecov Report

Merging #128 (ecfd35a) into main (a23d15f) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   99.73%   99.73%           
=======================================
  Files          51       51           
  Lines        1494     1494           
  Branches      320      321    +1     
=======================================
  Hits         1490     1490           
  Misses          4        4           

Impacted Files	Coverage Δ
src/lib/errors/CombinedError.ts	100.00% <100.00%> (ø)
src/lib/errors/CombinedPropertyError.ts	100.00% <100.00%> (ø)
src/lib/errors/ExpectedConstraintError.ts	100.00% <100.00%> (ø)
src/lib/errors/ExpectedValidationError.ts	100.00% <100.00%> (ø)
...lib/errors/MultiplePossibilitiesConstraintError.ts	100.00% <100.00%> (ø)
src/lib/errors/UnknownPropertyError.ts	100.00% <100.00%> (ø)
src/lib/errors/ValidationError.ts	100.00% <100.00%> (ø)

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[kyranet]

This needs updating too:

shapeshift/package.json

Line 74 in a23d15f

"node": ">=v15.0.0",