Specify host cli option

I normally do all my JS coding from my home server.  This PR enables to
to run the dev + hot client server correctly.

cli.js

@@ -30,6 +30,7 @@ const cli = meow(`
 
     ${chalk.gray('Dev server options')}
 
+      -h --host     Dev server host
       -p --port     Dev server port
       --no-open     Prevent from opening in default browser
 
@@ -51,6 +52,10 @@ const cli = meow(`
       type: 'string',
       alias: 'p'
     },
+    host: {
+      type: 'string',
+      alias: 'h'
+    },
     open: {
       type: 'boolean',
       alias: 'o',
@@ -83,6 +88,7 @@ const opts = Object.assign({
   globals: {
     FILENAME: JSON.stringify(path.resolve(doc))
   },
+  host: 'localhost',
   port: 8080,
   outDir: 'dist',
 }, config, cli.flags)
@@ -163,7 +169,8 @@ switch (cmd) {
     dev = require('./lib/dev')
     dev(opts)
       .then(res => {
-        const url = 'http://localhost:' + res.port
+        const { address, port } = res.server.address()
+        const url = 'http://' + address + ':' + res.port
         if (opts.open) open(url)
         log('listening on', chalk.magenta(url))
       })

lib/config.js

@@ -126,7 +126,8 @@ const createConfig = (opts = {}) => {
 
   const defs = Object.assign({}, opts.globals, {
     OPTIONS: JSON.stringify(opts),
-    HOT_PORT: JSON.stringify(opts.hotPort)
+    HOT_PORT: JSON.stringify(opts.hotPort),
+    HOT_HOST: JSON.stringify(opts.host)
   })
 
   config.plugins.push(

lib/dev.js

@@ -14,9 +14,11 @@ const devMiddleware = {
 
 const start = async (opts = {}) => {
   const app = new Koa()
+  opts.host = opts.host || 'localhost'
   opts.hotPort = await getPort()
   const hotClient = {
     port: opts.hotPort,
+    host: opts.host,
     logLevel: 'error'
   }
   opts.dirname = opts.dirname || path.dirname(opts.entry)
@@ -34,7 +36,7 @@ const start = async (opts = {}) => {
   app.use(middleware)
   app.use(koaStatic(opts.dirname))
 
-  const server = app.listen(port)
+  const server = app.listen(port, opts.host)
   return new Promise((resolve) => {
     middleware.devMiddleware.waitUntilValid(() => {
       resolve({ server, app, middleware, port })

lib/overlay.js

@@ -60,7 +60,7 @@ const destroy = () => {
   document.body.removeChild(overlay)
 }
 
-const ws = new WebSocket('ws://localhost:' + HOT_PORT)
+const ws = new WebSocket('ws://' + HOT_HOST + ':' + HOT_PORT)
 
 ws.addEventListener('message', msg => {
   const data = JSON.parse(msg.data)