Export default in vuex_shared/modal/actions

**Why?**
This prevents erros when using actions in karma test.

app/assets/javascripts/vuex_shared/modules/modal/actions.js

@@ -15,3 +15,6 @@ export const show = ({ commit }) => {
 export const hide = ({ commit }) => {
   commit(types.HIDE);
 };
+
+// prevent babel-plugin-rewire from generating an invalid default during karma tests
+export default () => {};