Fixed broken pandas guide link. (#81)

Author: Tomasz-Kluczkowski

pandas/index.html

@@ -540,7 +540,7 @@ <h4>During the sprint</h4>
 
                     <ul class="list-arrow-right">
                         <li>Go to the sprint location at the starting time</li>
-                        <li>Organizers will provide information, and there is <a href="https://python-sprints.github.io/pandas/guide/contents.html">documentation</a></li>
+                        <li>Organizers will provide information, and there is <a href="https://python-sprints.github.io/pandas/guide/index.html">documentation</a></li>
                         <li>Discuss on the <a href="https://gitter.im/py-sprints/pandas-doc">Gitter channel</a></li>
                         <li>Share your experience and photos in social networks using <b>#pandasSprint</b></li>
                         <li>Thank the local sponsor for their support (in person and in social media)</li>