Add 3.2 tags to supported version

This is the stable release, so we support all of GNOME Shell
stable cycle without updates.
(As said earlier, dock and alternate-tab have issues, so they're
not marked 3.2 but just 3.2.0)

extensions/example/metadata.json.in

@@ -2,7 +2,7 @@
  "uuid": "@uuid@",
  "name": "Hello, World!",
  "description": "An example extension to show how it works. Shows Hello, world when clicking on the top panel.",
- "shell-version": [ "@shell_current@" ],
+ "shell-version": [ "@shell_current@", "3.2" ],
  "localedir": "@LOCALEDIR@",
  "url": "@url@"
 }