Merge pull request #90 from erdomke/master

Initial Work on W3C Test Compliance

Source/External/ExCSS/Model/Selector/NthFirstChildSelector.cs

+
+// ReSharper disable once CheckNamespace
+namespace ExCSS
+{
+    internal sealed class NthFirstChildSelector : NthChildSelector, IToString
+    {
+        public override string ToString(bool friendlyFormat, int indentation = 0)
+        {
+            return FormatSelector(PseudoSelectorPrefix.PseudoFunctionNthchild);
+        }
+    }
+}
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