Update index.html (#1006)

make the url paths relative so that they work with url_prefixes as well.

Author: DavidiBeMe

apps/_default/static/index.html

@@ -31,9 +31,9 @@
       <img class="logo" src="/static/images/logo.png"/>
       <h1>PY4WEB</h1>
       <h2>Different, yet cute, and a memorable evolutionary step.</h2>
-      <a class="btn" href="/_dashboard">Dashboard</a>
-      <a class="btn" href="/_documentation">Documentation</a>
-      <a class="btn" href="/showcase">Examples</a>
+      <a class="btn" href="_dashboard">Dashboard</a>
+      <a class="btn" href="_documentation">Documentation</a>
+      <a class="btn" href="showcase">Examples</a>
       <a class="btn" href="https://learn-py4web.github.io/">Tutorials</a>
       <a class="btn" href="https://github.com/web2py/py4web">Source</a>
       <a class="btn" href="https://groups.google.com/forum/#!forum/py4web">Discuss</a>