update powered-by

index.html

@@ -77,6 +77,12 @@
             <a href="https://github.com/jacomyal/sigma.js">
                 <button class="indent collapse">jacomyal/sigma.js</button>
             </a>
+            <a href="https://github.com/chartjs/Chart.js">
+                <button class="indent collapse">chartjs/Chart.js</button>
+            </a>
+            <a href="https://github.com/showdownjs/showdown">
+                <button class="indent collapse">showdownjs/showdown</button>
+            </a>
             <a href="https://github.com/FortAwesome/Font-Awesome">
                 <button class="indent collapse">FortAwesome/Font-Awesome</button>
             </a>