chore: remove parentheses around site url (#1666)

As VSCode makes `http://localhost:8080/)` including trailing parentheses which leads to a 404.

packages/@vuepress/core/lib/node/webpack/DevLogPlugin.js

@@ -33,7 +33,7 @@ module.exports = class DevLogPlugin {
         + (
           isFirst
             ? ''
-            : `${chalk.gray(`(${displayUrl})`)}`
+            : `${chalk.gray(`${displayUrl}`)}`
         )
       )
       if (isFirst) {