[chrome-gnome-shell] readme: update Shell version

[Yuri Konotopov <ykonotopov src gnome org>]

commit 12dc618d261c4c50dd8203e5c194a99b97be89ff
Author: Yuri Konotopov <ykonotopov gnome org>
Date:   Tue May 22 20:44:34 2018 +0400

    readme: update Shell version

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 49f7ab2..7afc3e8 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ that provides integration with GNOME Shell and the corresponding extensions repo
 
 Requirements
 ------------
- * GNOME Shell up to 3.22
+ * GNOME Shell up to 3.28
  * Python 2.7+ or 3.x
  * PyGObject
  * Python Requests 2.x