Fix PCT Test (#498)

HtmlUnit does not appear to support the `[key]` syntax for setting
property IDs in ECMAScript objects. To work around this, use the built-
in `crumb.wrap` function from Jenkins core instead.

Author: mtughan

src/main/webapp/js/build.js

@@ -9,9 +9,7 @@ if (rebuildButton) {
     } else {
       fetch(buildUrl, {
         method: 'post',
-        headers: {
-          [document.head.dataset.crumbHeader]: document.head.dataset.crumbValue
-        }
+        headers: crumb.wrap({})
       })
         .then(res => {
           if (!res.ok) {