Fixed amp not rendering content

refs: 9d7049cd3

- I missed that the amp_content helper was meant to be async when refactoring
- I have updated our proper amp acceptance tests to catch the content not rendering as this is a regression, this should definitely have been caught
- Added missing async property to amp_content helper to fix the issue

core/frontend/apps/amp/lib/helpers/amp_content.js

@@ -201,3 +201,5 @@ function ampContent() {
 }
 
 module.exports = ampContent;
+
+module.exports.async = true;

test/frontend-acceptance/default_routes.test.js

@@ -208,8 +208,10 @@ describe('Default Frontend routing', function () {
 
                     $('style[amp-custom]').length.should.equal(1);
 
-                    res.text.should.containEql(':root {--ghost-accent-color: #FF1A75;}');
+                    // This asserts we should have some content (and not [object Promise] !)
+                    $('.post-content p').length.should.be.greaterThan(0);
 
+                    res.text.should.containEql(':root {--ghost-accent-color: #FF1A75;}');
                     res.text.should.not.containEql('__GHOST_URL__');
                 });
         });