Use fs from node instead of normalize/mz

[beckerei]

Is it still needed to support older node version that don't support readFile, writeFile?

mz ships with a dependancy to any-promise.

Are you willing to accept a PR to use nodes own implementation

[bcherny]

Hey there @beckerei! We use mz for the Promises. Since native Promise-based APIs were introduced pretty recently in Node 10, I'd like to stick with mz for now to support whatever Node version people might be using. Is there a particular issue you're running into due to the dependency on mz?

[beckerei]

Prior I thought it we had conflicts our test env, but then noticed the lib was not called during tests. So this was not an issue. Maybe others might have this problem at some point.