Add formatting to the helpUrl to avoid broken links

Since we're using the alpha release, the help urls generated are not live yet.
This commit fixes that by pointing at the 2.3.x release, and adds a message
that'll be noticed if someone updated axe in the future.

app/assets/javascripts/govuk_publishing_components/accessibility-test.js

@@ -31,7 +31,7 @@
         results.url + '\n\n' +
         violations.map(function (violation) {
           var help = 'Problem: ' + violation.help
-          var helpUrl = 'Try fixing it with this help: ' + violation.helpUrl
+          var helpUrl = 'Try fixing it with this help: ' + _formatHelpUrl(violation.helpUrl)
           var htmlAndTarget = violation.nodes.map(_renderNode).join('\n\n')
 
           return [
@@ -45,6 +45,14 @@
     })
   }
 
+  var _formatHelpUrl = function (helpUrl) {
+    if (axe.version.indexOf('alpha') === -1) {
+      console.warn('Deprecation warning: helpUrl formatting is no longer needed so can be deleted')
+      return helpUrl
+    }
+    return helpUrl.replace('3.0.0-alpha', '2.3')
+  }
+
   var _renderNode = function (node) {
     return (
       ' Check the HTML:\n' +