feat(hmr-ws-port): adds ability to explicitly set hmr ws port (#450)

* feat(hmr-ws-port): adds ability to explicitly set hmr ws port

* fix(conflict): fix merge conflict

* fix(hmr-ws-port): change args, misc cleanup

* fix(hmr-ws-port): add args to cli

src/Bundler.js

@@ -64,7 +64,8 @@ class Bundler extends EventEmitter {
         typeof options.minify === 'boolean' ? options.minify : isProduction,
       hmr: typeof options.hmr === 'boolean' ? options.hmr : watch,
       logLevel: typeof options.logLevel === 'number' ? options.logLevel : 3,
-      mainFile: this.mainFile
+      mainFile: this.mainFile,
+      hmrPort: options.hmrPort || 0
     };
   }
 
@@ -191,7 +192,7 @@ class Bundler extends EventEmitter {
 
     if (this.options.hmr) {
       this.hmr = new HMRServer();
-      this.options.hmrPort = await this.hmr.start();
+      this.options.hmrPort = await this.hmr.start(this.options.hmrPort);
     }
   }
 

src/HMRServer.js

@@ -2,9 +2,9 @@ const WebSocket = require('ws');
 const prettyError = require('./utils/prettyError');
 
 class HMRServer {
-  async start() {
+  async start(port) {
     await new Promise(resolve => {
-      this.wss = new WebSocket.Server({port: 0}, resolve);
+      this.wss = new WebSocket.Server({port}, resolve);
     });
 
     this.wss.on('connection', ws => {

src/cli.js

@@ -13,6 +13,11 @@ program
     'set the port to serve on. defaults to 1234',
     parseInt
   )
+  .option(
+    '-h, --hmr-port <port>',
+    'set the port to serve HMR websockets, defaults to random',
+    parseInt
+  )
   .option('--https', 'serves files over HTTPS')
   .option('-o, --open', 'automatically open in default browser')
   .option(