Minify meta refresh values

[stevenvachon]

<meta http-equiv="refresh" content="5; url=">
<meta http-equiv="refresh" content="5; url=http://example.com/">

can be shortened to:

<meta http-equiv="refresh" content="5">
<meta http-equiv="refresh" content="5; http://example.com/">

http-equiv-refresh

[SukkaW]

The HTML standard for meta[http-quiv="refresh"]: https://html.spec.whatwg.org/multipage/semantics.html#attr-meta-http-equiv-refresh