move xvfb-chromium binary path to config

package.json

@@ -8,7 +8,8 @@
     "DEFAULT_PUPPET": "web",
     "DEFAULT_PROFILE": "default-profile-name",
     "DEFAULT_PORT": 18788,
-    "DEFAULT_PUPPET_PORT": 28788
+    "DEFAULT_PUPPET_PORT": 28788,
+    "BINARY_CHROMIUM": "/wechaty/bin/xvfb-chromium"
   },
   "scripts": {
     "lint": "eslint src test || echo ok",

src/puppet-web/browser.js

@@ -108,8 +108,8 @@ class Browser extends EventEmitter {
     const options = {
       args: ['--no-sandbox']  // issue #26 for run inside docker
     }
-    if (process.env.WECHATY_DOCKER) {
-      options.binary = '/wechaty/bin/xvfb-chromium'
+    if (Config.isDocker) {
+      options.binary = Config.BINARY_CHROMIUM
     }
 
     const customChrome = WebDriver.Capabilities.chrome()