build(umd.js): renamed es modules to be .es.js files

[thkruz]

Originally changed .es.js to .js because of codecov issues. Ended up being caused by lack of .js.map
files. Reverting back for easier es-module identification

[codecov]

Codecov Report

Merging #17 (0d2fec2) into develop (e258121) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #17   +/-   ##
========================================
  Coverage    92.66%   92.66%           
========================================
  Files            5        5           
  Lines         1282     1282           
  Branches       103      103           
========================================
  Hits          1188     1188           
  Misses          94       94           

Impacted Files	Coverage Δ
src/ootk-multi.es.ts	38.00% <ø> (ø)
src/ootk-sgp4.es.ts	95.62% <ø> (ø)
src/ootk-transforms.es.ts	85.85% <ø> (ø)
src/ootk-utils.es.ts	100.00% <ø> (ø)

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