Doesn't work without webmidi

[fletcherist]

Hello! Thanks for the beautiful library!
You have mentioned in README

npm install --save tone
# optional
npm install --save webmidi

however If install only this package, and not installing webmidi, it fails with the following error message:

./node_modules/@tonejs/piano/build/midi/MidiInput.js
Module not found: Can't resolve 'webmidi' in '/Users/fletcherist/jamsandbox/node_modules/@tonejs/piano/build/midi'

is it yet optional or required? thanks in advance

[tambien]

It's required now. I'll update the README