bug: click to copy doc heading does not copy URL to clipboard

[barriebyron]

The Mina Docs have a nice click-to-copy subheading feature.

Good:

• the web browser URL is updated with the copied URL

Bad:

• the URL is not copied to the clipboard as expected

To reproduce, go to any topic and click to the right of any subheading. Result: the subheading URL address populates the web browser address field However, the URL is not copied to the clipboard as expected