Add core-js@2 dependency that is required by transpiled outputs of Babel

[texodus]

Rebased #757 on top of emscripten update fixes.

[codecov-io]

Codecov Report

Merging #758 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #758      +/-   ##
==========================================
+ Coverage   91.77%   91.87%   +0.09%     
==========================================
  Files          51       51              
  Lines        3162     3162              
==========================================
+ Hits         2902     2905       +3     
+ Misses        260      257       -3

Impacted Files	Coverage Δ
perspective/table/_date_validator.py	94.73% <0%> (+7.89%)	⬆️

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[texodus]

Thanks @sebinsua for the fix!