Update editor-style.css: switch style of sup & sub

[dujiulun]

Editor style for <sup> and <sub> are inversed, which causes <sup> to be subscript and vice versa. This commit fixes this bug.

[swissspidy]

Trac ticket for the issue: https://core.trac.wordpress.org/ticket/39812

Note that the build failed not because of the CSS change.

[afercia]

Can this issue have some traction please? 🙂 WordPress 4.8 is close to release, would be nice to fix this small, simple, issue.