feat: set exitCode to non-zero when catching error (close: #598 & #570) (#615)

Author: ulivz

bin/vuepress.js

@@ -103,6 +103,7 @@ function wrapCommand (fn) {
   return (...args) => {
     return fn(...args).catch(err => {
       console.error(chalk.red(err.stack))
+      process.exitCode = 1
     })
   }
 }