Don't lowercase attributes in html files

[DeMoorJasper]

↪️ Pull Request

Lowercasing html attributes breaks inline svg.

This PR changes the default to the posthtml default which is to not lowercase attributes.

💻 Examples

In the changed files you can see that the htmlnano test actually included broken inline svg code, due to the default previous to this pr.

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

[m5o]

Thanks to @DeMoorJasper for supporting on finding this issue.
SVG rendering is affected if viewBox attribute is converted to lowercase by posthtml.

-    <svg viewBox="0 0 32 32" v-bind:data-score="score">
+    <svg viewbox="0 0 32 32" v-bind:data-score="score">
       <circle v-bind:style="stroke" r="16" cx="16" cy="16" />
     </svg>

viewbox	viewBox

Full example

📺 https://codesandbox.io/s/5jo8oywok

Reference

🔗 #1523