message: [Doc] update site title
diff: @@ -4,7 +4,7 @@ module.exports = {
  header: {
  logo: {
  image: 'https://img.yzcdn.cn/public_files/2017/12/18/fd78cf6bb5d12e2a119d0576bedfd230.png',
  - title: 'Zan UI',
  + title: 'Vant',
  href: 'http://www.youzanyun.com/zanui'
  },
  nav: {
  @@ -282,7 +282,7 @@ module.exports = {
  header: {
  logo: {
  image: 'https://img.yzcdn.cn/public_files/2017/12/18/fd78cf6bb5d12e2a119d0576bedfd230.png',
  - title: 'Zan UI',
  + title: 'Vant',
  href: 'http://www.youzanyun.com/zanui'
  },
  nav: {
  