The `sizes` attribute was calculated incorrectly, resulting in the browser downloading the wrong resource. This filters the attribute to correct that.
Before the filter, the `img` contained:
`sizes="(max-width: 767px) 89vw, (max-width: 1000px) 54vw, (max-width: 1071px) 543px, 580px"`
And after:
`sizes="100vw"`
Props joemcgill, transl8or.
Fixes#38847.
Built from https://develop.svn.wordpress.org/trunk@39291
git-svn-id: http://core.svn.wordpress.org/trunk@39231 1a063a9b-81f0-0310-95a4-ce76da25c4cd