Remove link since in its current form it's invalid HTML

examples/classic-slides/index.html

@@ -325,7 +325,7 @@
           A(Support for<br />diagrams)
           B[Provided by<br />mermaid.js]
           C{Already<br />know<br />mermaid?}
-          D(<a href=&quot;http://knsv.github.io/mermaid/index.html#usage&quot;>Tutorial</a>)
+          D(Tutorial)
           E(Great, hope you enjoy!)
           A-->B
           B-->C