Coverpage link bug in >= 4.8.1

[dbanksdesign]

Here is my coverpage markdown file: https://github.com/amzn/style-dictionary/blob/master/docs/_coverpage.md

I noticed the github button styling broke in recent versions. I rolled back to 4.8.0 and they work again. Here is the issue that was filed on our repo: amzn/style-dictionary#185

It looks like the docsify parser was not adding data-button to the github link for some reason. And the stylesheet in <= 4.8.0 was not targeting data-button to style those buttons.

[QingWei-Li]

v4.8.4 is released.