[modulizer] wct-browser-legacy does not pass yarn install --flat

[web-padawan]

Running yarn install --flat without a lockfile results in the following error:

warning wct-browser-legacy > mocha > mkdirp@0.5.1: Legacy versions of mkdirp are no longer supported. Please update to mkdirp 1.x. (Note that the API surface has changed to use Promises in 1.x.)
info Unable to find a suitable version for "es-abstract", please choose one by typing one of the numbers below:
  1) "es-abstract@^1.17.4, es-abstract@^1.17.5, es-abstract@^1.17.5, es-abstract@^1.17.5" which resolved to "1.17.6"
  2) "es-abstract@^1.18.0-next.0" which resolved to "1.18.0-next.0"

The solution would be to add es-abstract to the "resolutions" section. I can submit a PR for that.

[stale]

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