Generator fails when browserslist >= 4.8.4 installed

[outoftime]

Reduction

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When invoking generateData() with browserslist 4.8.4 or newer installed, the following error obtains:

TypeError: Cannot read property 'x' of undefined
    at generatePrefixMap (/home/runner/DefiantOpaqueEmulation/node_modules/inline-style-prefixer/lib/generator/generatePrefixMap.js:54:31)
    at generateData (/home/runner/DefiantOpaqueEmulation/node_modules/inline-style-prefixer/lib/generator/index.js:74:71)
    at /home/runner/DefiantOpaqueEmulation/index.js:6:30    at Script.runInContext (vm.js:133:20)
    at Object.<anonymous> (/run_dir/interp.js:156:20)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)

I believe this is because ie_mob is hard-coded into the prefixBrowserMap but as of browserslist 4.8.4 it is no longer returned by queries, presumably because it was marked as a dead browser in this commit.

As a workaround, downgrading to browserslist 4.8.3 fixes the error.

[robinweser]

Would you be willing to send a PR that removes ie_mob? I believe it mostly mirrors IE anyways and given its usage it is kinda dead for sure.