Add new extension slider (#1108)

docs/extensions.html

@@ -3,6 +3,11 @@ title: Extensions
 layout: default
 route: extensions
 extensions:
+- name: bulma-slider
+  url: https://github.com/Wikiki/bulma-slider
+  slug: bulma-slider
+  width: 1119
+  height: 158
 - name: bulma-checkradio
   url: https://github.com/Wikiki/bulma-checkradio
   slug: bulma-checkradio