feat(core): add --open argument to open browser automatically (close: #1100)(#1109)

Author: Dmitriy Sharshakov aka. sh7dm

packages/@vuepress/core/lib/dev.js

@@ -121,6 +121,7 @@ module.exports = async function dev (sourceDir, cliOptions = {}) {
     },
     logLevel: 'error',
     port,
+    open: cliOptions.open,
     add: app => {
       // apply plugin options to extend dev server.
       ctx.pluginAPI.options.enhanceDevServer.syncApply(app)

packages/vuepress/lib/registerCoreCommands.js

@@ -22,6 +22,7 @@ module.exports = function (cli, options) {
     .option('--no-cache', 'clean the cache before build')
     .option('--debug', 'start development server in debug mode')
     .option('--silent', 'start development server in silent mode')
+    .option('--open', 'open browser when ready')
     .action((sourceDir = '.', commandOptions) => {
       const { debug, silent } = commandOptions