Twenty Fifteen: update editor styles to better account for adaptive images in small screens.

See #31934, props iamtakashi.

git-svn-id: https://develop.svn.wordpress.org/trunk@32090 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentyfifteen/css/editor-style.css

@@ -486,7 +486,7 @@ body.rtl {
  * 9.0 Media Queries
  */
 
-@media screen and (max-width: 660px) {
+@media screen and (max-width: 740px) {
 	body, img, .wp-caption {
 		max-width: 100%;
 	}