Usage with webpack5's new `cache.type = 'filesystem'` seems broken across builds.

[erlandsona]

Webpack has a new cache: { type: 'filesystem' } which elm-webpack-loader doesn't seem to be busting properly.

When I run webpack the first time it builds all the Elm code for the project. Then after making a change to any of the Elm code and running webpack subsequent times seem to "re-use" the cache even tho there have been changes to the Elm code.

Preferably elm-webpack-loader would support this use case.