[meld] README: Bump our documented GtkSourceView requirement

[Kai Willadsen <kaiw src gnome org>]

commit e0d898768f23ebc9f72933162e2ec0480475e2e4
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Thu Aug 15 06:53:18 2019 +1000

    README: Bump our documented GtkSourceView requirement

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 8d0f6aed..e5c8394a 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@ And following packages with GObject introspection:
 * Pango
 * PangoCairo
 * GTK+ 3.20
-* GtkSourceView 3.20 (note that GtkSourceView 4 is not supported)
+* GtkSourceView 4.0
 
 
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