Twenty Seventeen: Additional default header image optimizations.

This is a follow-up to [39248] that applies a bit more compression to
the default header image in Twenty Seventeen.

Props Presskopp, lukecavanagh.
Fixes #38793.
Built from https://develop.svn.wordpress.org/trunk@39279


git-svn-id: http://core.svn.wordpress.org/trunk@39219 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-beta4-39278';
+$wp_version = '4.7-beta4-39279';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.