Change "Gittip" -> "Gratipay" and update widget accordingly

app/views/pages/contributing.html.slim

@@ -45,14 +45,14 @@
       = image_tag 'bitcoin-logo.png', class: 'bitcoin-logo'
       a href="bitcoin:1GLaEx3cU5rzaMVhst1djCJvs5HK8PAsV4?amount=0.05&label=Asciinema%20donation" 1GLaEx3cU5rzaMVhst1djCJvs5HK8PAsV4 
 
-    h3 Gittip
+    h3 Gratipay
 
     p
-      ' Gittip is a way to give small weekly cash gifts to people you love and
+      ' Gratipay is a way to give small weekly cash gifts to people you love and
         are inspired by. And it's great for supporting open-source authors and
-        projects. To donate to Asciinema via Gittip, click on the button below.
+        projects. To donate to Asciinema via Gratipay, click on the button below.
 
-    <script data-gittip-username="sickill" data-gittip-widget="button" src="//gttp.co/v1.js"></script>
+    <script data-gratipay-username="sickill" data-gratipay-widget="button" src="//grtp.co/v1.js"></script>
 
     h3 PayPal