Instantiate using the concrete type SimpleHighlightingBrush

The type `HighlightingBrush` is abstract and cannot be instantiated. `SimpleHighlightingBrush` is what we want.

Author: richardbuckle

ICSharpCode.AvalonEdit/Highlighting/HighlightingColor.cs

@@ -196,8 +196,8 @@ protected HighlightingColor(SerializationInfo info, StreamingContext context)
 				this.Underline = info.GetBoolean("Underline");
 			if (info.GetBoolean("HasStrikethrough"))
 				this.Strikethrough = info.GetBoolean("Strikethrough");
-			this.Foreground = (HighlightingBrush)info.GetValue("Foreground", typeof(HighlightingBrush));
-			this.Background = (HighlightingBrush)info.GetValue("Background", typeof(HighlightingBrush));
+			this.Foreground = (HighlightingBrush)info.GetValue("Foreground", typeof(SimpleHighlightingBrush));
+			this.Background = (HighlightingBrush)info.GetValue("Background", typeof(SimpleHighlightingBrush));
 			if (info.GetBoolean("HasFamily"))
 				this.FontFamily = new FontFamily(info.GetString("Family"));
 			if (info.GetBoolean("HasSize"))