conditionally set displayUrl to https

Originally, the `displayUrl` output in log messages was hard-coded to be `http`. Now it is set to `https` if the `isHttps` value passed in via `options` is truthy.

Author: morphatic

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

@@ -17,15 +17,15 @@ module.exports = class DevLogPlugin {
 
  apply (compiler) {
  let isFirst = true
- const { displayHost, port, publicPath, clearScreen: shouldClearScreen } = this.options
+ const { displayHost, port, publicPath, clearScreen: shouldClearScreen, isHttps } = this.options
 
  compiler.hooks.done.tap('vuepress-log', stats => {
  if (shouldClearScreen) {
  clearScreen()
  }
 
  const time = new Date().toTimeString().match(/^[\d:]+/)[0]
- const displayUrl = `http://${displayHost}:${port}${publicPath}`
+ const displayUrl = `http${isHttps ? 's' : ''}://${displayHost}:${port}${publicPath}`
 
  logger.success(
  `${chalk.gray(`[${time}]`)} Build ${chalk.italic(stats.hash.slice(0, 6))} `