[gnome-shell-extensions] build: Fix description of the `enable_extensions` option

[Iñigo Martínez <inigomartinez src gnome org>]

commit 9dc183af231fd31a02f198c675ae6d81ced2a5ec
Author: Iñigo Martínez <inigomartinez gmail com>
Date:   Wed Dec 20 17:41:24 2017 +0100

    build: Fix description of the `enable_extensions` option
    
    The description of the `enable_extensions` was wrong since it
    changed to the `array` type, because the extension separator
    is now a comma instead of space.

 meson_options.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson_options.txt b/meson_options.txt
index 8d2eaf8..d721a49 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -8,7 +8,7 @@ option('extension_set',
 option('enable_extensions',
   type: 'array',
   value: [],
-  description: 'Space separated list of extensions to enable instead of a predefined set.'
+  description: 'Comma separated list of extensions to enable instead of a predefined set.'
 )
 
 option('classic_mode',