[gtk] Fix a doc comment

[Matthias Clasen <matthiasc src gnome org>]

commit be2ba89900845fb4ef244c0dcc6b52c254e2c39c
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Feb 8 19:27:32 2020 -0500

    Fix a doc comment
    
    Signals take two colons.

 gdk/gdkcontentprovider.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gdk/gdkcontentprovider.c b/gdk/gdkcontentprovider.c
index 8ae97d4a40..e4c6afda45 100644
--- a/gdk/gdkcontentprovider.c
+++ b/gdk/gdkcontentprovider.c
@@ -199,7 +199,7 @@ gdk_content_provider_class_init (GdkContentProviderClass *class)
                         G_PARAM_EXPLICIT_NOTIFY);
 
   /**
-   * GdkContentProvider:content-changed:
+   * GdkContentProvider::content-changed:
    *
    * Emitted whenever the content provided by this provider has changed.
    */