fix(webpack): use static babel config

[gregberge]

Fixes #232

[vercel]

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[codecov]

Codecov Report

Merging #240 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #240      +/-   ##
==========================================
+ Coverage   85.36%   85.43%   +0.06%     
==========================================
  Files          29       29              
  Lines         451      453       +2     
  Branches      127      127              
==========================================
+ Hits          385      387       +2     
  Misses         55       55              
  Partials       11       11

Impacted Files	Coverage Δ
packages/rollup/src/index.js	100% <100%> (ø)	⬆️
packages/webpack/src/index.js	95.65% <100%> (+0.19%)	⬆️

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