[examples] Fix HTML end tag

[raybooysen]

• I have followed (at least) the PR section of the contributing guide.

[mui-pr-bot]

Details of bundle changes.

Comparing: 784c0a2...c2eff6a

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	0.00%	0.00%	347,568	347,568	89,893	89,893
@material-ui/core/Paper	0.00%	0.00%	68,404	68,404	20,053	20,053
@material-ui/core/Paper.esm	0.00%	0.00%	60,735	60,735	18,785	18,785
@material-ui/core/Popper	0.00%	0.00%	34,930	34,930	11,917	11,917
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	17,877	17,877	5,962	5,962
@material-ui/core/useMediaQuery	0.00%	0.00%	2,463	2,463	1,044	1,044
@material-ui/lab	0.00%	0.00%	148,119	148,119	43,913	43,913
@material-ui/styles	0.00%	0.00%	53,143	53,143	15,443	15,443
@material-ui/system	0.00%	0.00%	17,132	17,132	4,519	4,519
Button	0.00%	0.00%	88,669	88,669	26,423	26,423
Modal	0.00%	0.00%	82,688	82,688	24,802	24,802
colorManipulator	0.00%	0.00%	3,745	3,745	1,537	1,537
docs.landing	0.00%	+0.02% 🔺	49,820	49,822	10,807	10,809
docs.main	0.00%	0.00%	644,630	644,634	200,877	200,879
packages/material-ui/build/umd/material-ui.production.min.js	0.00%	0.00%	296,257	296,257	82,811	82,811

Generated by 🚫 dangerJS against c2eff6a

[oliviertassinari]

The correct version is:

<link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons">

We should fix the other links. https://www.w3.org/TR/html5/document-metadata.html#the-link-element

[oliviertassinari]

create react app used to do it correctly before: facebook/create-react-app#5839.

[eps1lon]

• self closing void elements (Content Model: nothing) are valid html5

Then, if the element is one of the void elements, or if the element is a foreign element, then there may be a single U+002F SOLIDUS character (/). This character has no effect on void elements, but on foreign elements it marks the start tag as self-closing.

--https://www.w3.org/TR/html5/syntax.html#start-tags

• prettier formats it that way
• it's closer to react
• matches our current approach

[oliviertassinari]

Well, I have looked at Amazon & Facebook HTML response from the server they add a leading /> (Google doesn't). I guess we can follow them. It will soften the different between HTML and JSX