Move mutator actions to a special file just for mutators

app/assets/javascripts/mr_notes/stores/actions.js

-import types from './mutation_types';
-
-export default {
-  setActiveTab({ commit }, tab) {
-    commit(types.SET_ACTIVE_TAB, tab);
-  },
-};
+export * from './actions/mutators';

app/assets/javascripts/mr_notes/stores/actions/mutators.js

+import types from '../mutation_types';
+
+// Actions that exclusively mutate the state (essentially wrappers for `commit`)
+
+export function setActiveTab({ commit }, tab) {
+  commit(types.SET_ACTIVE_TAB, tab);
+}

app/assets/javascripts/mr_notes/stores/modules/index.js

-import actions from '../actions';
+import * as actions from '../actions';
 import getters from '../getters';
 import mutations from '../mutations';