Add 'button' role to link button template

Another of the changes pulled in in the latest
template is that links with a role="button" can be targeted
by a script that will treat them the same as buttons.
This means you can press the space bar when they're focused
and it should register a click.

Frontend apps will have to set up their javascript independently,
but the button role will be in the markup from now on.

Source: alphagov/govuk_frontend_toolkit#297

pages_builder/assets/javascripts/onready.js

@@ -32,6 +32,12 @@
     GOVUK.GDM.validation();
   }
 
+  if (GOVUK.shimLinksWithButtonRole) {
+    GOVUK.shimLinksWithButtonRole.init({
+      selector: '.link-button'
+    });
+  }
+
   if (GOVUK.ShowHideContent) {
     var showHideContent = new GOVUK.ShowHideContent()
     showHideContent.init()

pages_builder/pages/link-button.yml

@@ -2,6 +2,8 @@ pageTitle: Link buttons
 assetPath: ../govuk_template/assets/
 head: >
   <link rel="stylesheet" media="all" type="text/css" href="../public/stylesheets/index.css" />
+bodyEnd: >
+  <script type="text/javascript" src="../public/javascripts/govuk_frontend_toolkit/govuk/shim-links-with-button-role.js"></script>
 examples:
   -
     label: View service

toolkit/templates/link-button.html

@@ -1 +1 @@
-<a class='link-button{% if advice %}-with-advice{% endif %}' href='{{ url }}'>{{ label }}</a>
+<a class='link-button{% if advice %}-with-advice{% endif %}' href='{{ url }}' role='button'>{{ label }}</a>