Add missing isComposer computed property

assets/javascripts/discourse/components/wizard-custom-field.js.es6

@@ -17,6 +17,7 @@ export default Component.extend(UndoChanges, {
   isText: equal('field.type', 'text'),
   isTextarea: equal('field.type', 'textarea'),
   isUrl: equal('field.type', 'url'),
+  isComposer: equal('field.type', 'composer'),
   showPrefill: or('isText', 'isCategory', 'isTag', 'isGroup', 'isDropdown'),
   showContent: or('isCategory', 'isTag', 'isGroup', 'isDropdown'),
   showLimit: or('isCategory', 'isTag'),