Fixed xyChart.html link and renamed xyChart.md to xychart.md

demos/index.html

@@ -61,7 +61,7 @@ <h2><a href="./pie.html">Pie</a></h2>
         <h2><a href="./quadrantchart.html">Quadrant charts</a></h2>
       </li>
       <li>
-        <h2><a href="./xychart.html">XY charts</a></h2>
+        <h2><a href="./xyChart.html">XY charts</a></h2>
       </li>
       <li>
         <h2><a href="./requirements.html">Requirements</a></h2>