chore: Upgrade Babel, Jest, Eslint (#1437)

* chore: Upgrade Prettier 1.8 -> 2.0

* chore: Upgrade Babel 6 -> 7

* chore: Upgrade eslint plugins

* chore: Add eslint import/order rules

* chore: Update flow-typed deps

server/services/websockets.js

@@ -1,4 +1,6 @@
 // @flow
+import subHours from "date-fns/sub_hours";
+import { socketio } from "../";
 import type { Event } from "../events";
 import {
   Document,
@@ -7,9 +9,7 @@ import {
   CollectionGroup,
   GroupUser,
 } from "../models";
-import { socketio } from "../";
 import { Op } from "../sequelize";
-import subHours from "date-fns/sub_hours";
 
 export default class Websockets {
   async on(event: Event) {