[gxml] Fix prefix for schema namespace

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit 7f25ff4b96dc19d5b6105887c20c68eddff1b795
Author: Daniel Espinosa <esodan gmail com>
Date:   Thu Feb 27 08:38:26 2020 -0600

    Fix prefix for schema namespace
    
    Thanks to Daniel Mustieles García

 gxml/Element.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gxml/Element.vala b/gxml/Element.vala
index cc1250b..96de89d 100644
--- a/gxml/Element.vala
+++ b/gxml/Element.vala
@@ -721,7 +721,7 @@ public class GXml.Element : GXml.Node,
     }
     if (p == "xsi" && namespace_uri != "http://www.w3.org/2001/XMLSchema-instance/";
             && namespace_uri != "http://www.w3.org/2001/XMLSchema-instance";) {
-       throw new DomError.NAMESPACE_ERROR (_("Invalid namespace. If attribute's prefix is 'html', namespace 
URI should be http://www.w3.org/2001/XMLSchema-instance";));
+       throw new DomError.NAMESPACE_ERROR (_("Invalid namespace. If attribute's prefix is 'xsi', namespace 
URI should be http://www.w3.org/2001/XMLSchema-instance";));
     }
     if (p.down () == "mathml" && namespace_uri != "http://www.w3.org/1998/Math/MathML/";
             && namespace_uri != "http://www.w3.org/1998/Math/MathML";) {