Fix tests

[sindresorhus]

Something is broken with Spectron.

electron-serve/package.json

Lines 13 to 14 in 9636bee

	"test": "xo",
	"//test": "xo && (cd test && ava) && tsd"

[mhkeller]

I noticed when running the tests that you can't npm install on newer macs since it seems there is no version of Electron 8 that runs on Apple Silicon.