Update SkipTo.js to fix Alt+0 shortcut for non-english keyboards on macOS

[jongund]

I have fixed a bug in SkipTo.js for the shortcut key alt+0 for Apple macOs computers using a non-english keyboard arrangement.

The latest version of SkipTo.js can be found:

https://skipto-landmarks-headings.github.io/page-script-5/dist/skipto.js

Minified:
https://skipto-landmarks-headings.github.io/page-script-5/dist/skipto.min.js

SkipTo Issue:
skipto-landmarks-headings/page-script-5#11