Use typesVersions to provide types for ts <4.x

[mmkal]

Uses downlevel-dts to generate ts 3.4.x compatible types

This is a better fix for #250 than #251, and will also allow using more ts>4 features like named tuple types.

[codecov-io]

Codecov Report

Merging #253 (f8d7e3d) into master (cd44850) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #253   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines           59        59           
  Branches         7         7           
=========================================
  Hits            59        59           

Impacted Files	Coverage Δ
src/node_redis/multi.ts	100.00% <ø> (ø)

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