[docs] Fix i18n page transition

[li-yechao]

No description provided.

[oliviertassinari]

@unordered How we can reproduce the issue?

[li-yechao]

@oliviertassinari
checkout from master
yarn install
yarn start
open left menu and click anyone

TypeError: Cannot read property 'offsetTop' of null
AppTableOfContents._this.findActiveIndex
./docs/src/modules/components/AppTableOfContents.js:130

  127 | 
  128 | for (let i = 0; i < this.itemsClient.length; i += 1) {
  129 |   const item = this.itemsClient[i];
> 130 |   if (
  131 |     document.documentElement.scrollTop < item.node.offsetTop + 100 ||
  132 |     i === this.itemsClient.length - 1
  133 |   ) {

Try more times if no error.

[oliviertassinari]

What browser do you use?

[li-yechao]

chrome with latest version

[joshwooding]

I’ve never had this issue

[oliviertassinari]

@joshwooding Change the language then change the page, you will see the error. I'm having a look at it.

[oliviertassinari]

@unordered It's a great first pull request on Material-UI 👌🏻. Thank you for working on it!

[li-yechao]

@oliviertassinari it's my honor