Changed overflow: visible to overflow: hidden for hr element

[costingh]

Applied the expected overflow value for hr element, accordingly to HTML5 spec

[nuxodin]

Do you have a link to the spec? I can't find anything regarding css overflow.

[costingh]

Do you have a link to the spec? I can't find anything regarding css overflow.

This is the link to the spec: https://html.spec.whatwg.org/multipage/rendering.html#the-hr-element-2

[nosilleg]

fixes #860