Update webpack-dev-server & babel version in TeX examples (#1981)

Summary:
**Summary**
* Upgrade `webpack-dev-server` to 3.1.14 to fix [vulnerability in versions < 3.1.11](https://nvd.nist.gov/vuln/detail/CVE-2018-14732) & `webpack` to 4.0.0 to match it
* Upgrade `babel` to 6.0.0 & `babel-loader` to 7.0.0 to match `webpack` upgrade
* Changes to `server.js` & `app.js` to support the `webpack` & `babel` version upgrades

**Test Plan**
Run `yarn start` and load http://localhost:3000/
<img width="1089" alt="screenshot 2019-01-21 13 22 30" src="https://user-images.githubusercontent.com/2357761/51502558-5974d780-1d8b-11e9-8568-917f43967188.png">
Pull Request resolved: facebookarchive/draft-js#1981

Reviewed By: claudiopro

Differential Revision: D13754649

Pulled By: claudiopro

fbshipit-source-id: 19169f9b091d85344d975e2d7b963437b7701e9b

examples/draft-0-10-0/tex/js/app.js

@@ -14,7 +14,6 @@
 
 'use strict';
 
-import 'babel/polyfill';
 import TeXEditorExample from './components/TeXEditorExample';
 import React from 'react';
 import ReactDOM from 'react-dom';

examples/draft-0-10-0/tex/package.json

@@ -4,9 +4,9 @@
     "start": "babel-node ./server.js"
   },
   "dependencies": {
-    "babel": "5.8.23",
+    "babel": "6.0.0",
     "babel-core": "^6.8.0",
-    "babel-loader": "^6.2.4",
+    "babel-loader": "^7.0.0",
     "babel-preset-es2015": "^6.9.0",
     "babel-preset-react": "^6.11.1",
     "draft-js": "file:../../../",
@@ -15,8 +15,8 @@
     "katex": "^0.5.1",
     "react": "file:../../../node_modules/react",
     "react-dom": "file:../../../node_modules/react-dom",
-    "webpack": "^1.10.5",
-    "webpack-dev-server": "^1.10.1"
+    "webpack": "^4.0.0",
+    "webpack-dev-server": "^3.1.14"
   },
   "devDependencies": {
     "babel-cli": "^6.18.0"

examples/draft-0-10-0/tex/server.js

@@ -23,18 +23,19 @@ const APP_PORT = 3000;
 var compiler = webpack({
   entry: path.resolve(__dirname, 'js', 'app.js'),
   module: {
-    loaders: [
+    rules: [
       {
         test: /\.js$/,
         exclude: /node_modules/,
-        loader: 'babel',
-        query: {
+        loader: 'babel-loader',
+        options: {
           presets: ['es2015', 'react'],
         },
       },
     ],
   },
   output: {filename: 'app.js', path: '/'},
+  mode: 'development',
 });
 var app = new WebpackDevServer(compiler, {
   contentBase: '/public/',