[css-grid-3] Tweak spec metadata.

Author: heycam

css-grid-3/Overview.bs

@@ -1,10 +1,11 @@
 <pre class='metadata'>
-Title: CSS Masonry Layout Module
+Title: CSS Grid Layout Layout Module Level 3
 Shortname: css-grid-3
-Status: LS
-Work Status: Testing
-Level: none
-URL: https://drafts.csswg.org/css-grid-3/
+Level: 3
+Status: ED
+Work Status: Exploring
+Group: csswg
+ED: https://drafts.csswg.org/css-grid-3/
 Editor: Tab Atkins Jr., Google, http://www.xanthir.com/contact/, w3cid 42199
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
 Editor: Mats Palmgren, Mozilla, mailto:mats@mozilla.com