ignorePattern doesn't seem to be working

Howdy 👋

Just trying to stop this gzipping my sourcemaps and I've been trying to add an ignorePattern that doesn't seem to be working 😕

I've tried `ignorePattern: '**.map'` and `ignorePattern: '*.map'` but they both still gzipped my sourcemaps. I even tried `ignorePattern: '\*\*/\*.map',` which I lifted from the default filePattern 😂

I ended up working around this by just using filePattern with `map` removed as an option, but I figured I should open an issue to see if there is anything I can do to help. I would love to add a failing test if someone could at least point me in the right direction.