Update error text to match required Wayland version

The required Wayland version was updated to 1.1, but the top-level error
message was not updated to reflect this.

Change-Id: Ifc1c7552a4a38986685c214e24241704fd774e11
Reviewed-by: Jan Arne Petersen <jan.petersen@kdab.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>