Update JavaScript documentation

- discovered during testing that if the thing passed to the event listener is the same name as the function it ultimately calls, Jasmine gets confused when trying to apply spyOn

docs/javascript-modules.md

@@ -52,13 +52,13 @@ AnExampleModule.prototype.init = function ($module) {
   if (consentCookie && consentCookie.usage) {
     this.startModule()
   } else {
-    this.startModule = this.startModule.bind(this)
-    window.addEventListener('cookie-consent', this.startModule)
+    this.start = this.startModule.bind(this)
+    window.addEventListener('cookie-consent', this.start)
   }
 }
 
 AnExampleModule.prototype.startModule = function () {
-  window.removeEventListener('cookie-consent', this.startModule)
+  window.removeEventListener('cookie-consent', this.start)
   // the rest of the module
 }
 ```