website: Fix Contributing card link

The contributing page url doesn't end with "/".

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: I9936729e5bc2cb17c4c3d3305a02332ca6a9e6b2
diff --git a/index.html b/index.html
index c7e20f3..6ca524e 100755
--- a/index.html
+++ b/index.html
@@ -50,7 +50,7 @@
         <div class="card-body">
           <h5 class="card-title">Contributing</h5>
           <p class="card-text">Aid the gem5 project by becoming a contributor!</p>
-          <a href="/contributing/" class="btn btn-primary">Go to Contributing</a>
+          <a href="/contributing" class="btn btn-primary">Go to Contributing</a>
         </div>
       </div>
     </div>