Add "Repository" metadata (#306)

Per Tab: "Given the recent change to webapps boilerplate, need to specify Repository to get the right output on some of the links."

Author: tabatkins

index.bs

@@ -16,6 +16,7 @@ Level: 3
 Editor: Ali Alabbas, Microsoft Corp. https://microsoft.com, [email protected]
 Editor: Joshua Bell, Google Inc. https://google.com, [email protected]
 Group: webapps
+Repository: w3c/IndexedDB
 Test Suite: https://github.com/web-platform-tests/wpt/tree/master/IndexedDB
 Favicon: logo-db.png
 Complain About: accidental-2119 yes