Cleanup dist before build

[davidkopp]

Currently, when a note is moved or renamed, the old file is not deleted. Therefore I recommend to do a cleanup before the build.

Executing npm run build executes prebuild as the first step.

[oleeskild]

Nice, thanks! Do you think it would be possible to make a solution that would also work on windows, that way it won't crash if anyone tries to run it locally on their windows machine 😄

[davidkopp]

I have changed it to use rimraf, rm -rf for node in a cross-platform implementation.