Use Hidden as default SvgOverflow value

- changes behavior to be as described in this file and in the W3C test
masking-path-03-b
- fixes that test
- this has been a regression after removing the unconditional clip box
for every view box, (see #279)

Source/DataTypes/SvgOverflow.cs

@@ -21,6 +21,9 @@ namespace Svg
     [TypeConverter(typeof(SvgOverflowConverter))]
 	public enum SvgOverflow
     {
+        /// <summary>Overflow is not rendered.</summary>
+        Hidden,
+
         /// <summary>The value is inherited from the parent element.</summary>
 		Inherit,
 
@@ -30,9 +33,6 @@ namespace Svg
         /// <summary>Overflow is rendered.</summary>
         Visible,
 
-        /// <summary>Overflow is not rendered.</summary>
-        Hidden,
-
         /// <summary>Overflow causes a scrollbar to appear (horizontal, vertical or both).</summary>
 		Scroll
 	}