Omit type attributes for style sheets and scripts

[jonasspott]

Info from https://passmarked.com/

<!-- Not recommended -->
<link rel="stylesheet" href="//www.google.com/css/maia.css" type="text/css">
<!-- Recommended -->
<link rel="stylesheet" href="//www.google.com/css/maia.css">

Info:
https://google.github.io/styleguide/htmlcssguide.xml

[owais]

Sounds good. Feel free to send a PR to fix it. Thanks.

[fjsj]

Fixed by #170