Update npm instructions to point to 1.3.7

[sliechti]

[email protected] is being promoted here:

https://quilljs.com/docs/download/ https://github.com/quilljs/quill/blob/develop/docs/docs/download.md

Which has the following advisory: https://www.npmjs.com/advisories/1039

I'd suggest updating to promote 1.3.7.