build: enable production mode

[merceyz]

What's the problem this PR addresses?

Corepack is built in Webpack's development mode which causes Webpack to output files with long filenames.

Fixes #130

How did you fix it?

Change it to build in production mode but disable minimizing so the code is still somewhat readable.

The bundle size also improved a bit:

$ du -s dist
- 2434    dist
+ 2170    dist

[styfle]

Removing terser should probably be a separate PR since its not related to production mode.

I think its acceptable to merge the production change because that fixes a bug. But removing terser is more of a preference and might require further discussion.

[merceyz]

But removing terser is more of a preference and might require further discussion.

In development mode it didn't do anything and this PR preserves that by disabling it with minimize: false, therefore the new TerserPlugin code was unnecessary so I removed it.

[arcanis]

LGTM; I probably misunderstood whether development mode would respect or not explicit optimization settings.