Make Hogan definition clearer in radioSelect JS

It helps the tests to know the `Hogan` variable is
actually a property of the global variable
(`window` in this case) and doesn't hurt the
readability of the script.

app/assets/javascripts/radioSelect.js

@@ -1,7 +1,10 @@
-(function(Modules) {
+(function(global) {
 
   "use strict";
 
+  var Modules = global.GOVUK.Modules;
+  var Hogan = global.Hogan;
+
   let states = {
     'initial': Hogan.compile(`
       <div class="radio-select-column">
@@ -151,4 +154,4 @@
 
   };
 
-})(window.GOVUK.Modules);
+})(window);