Bug report

Describe the bug

When running next using Yarn 2 and visiting a page in the browser that doesn't exist, the 404 error page never shows up. Instead it loads forever ("waiting on localhost...") and then eventually errors with ERR_EMPTY_RESPONSE.

But the terminal shows that the page was compiled:

[ event ] build page: /next/dist/pages/_error
[ wait ]  compiling ...

Summary

Our docs relating to GraphQL sometimes have CodeSandbox samples where viewers can edit their query. However, these pages are represented in the markdown as raw iframes and are quite ugly:

<iframe title="A basic query" src="https://7118

I think this would be very useful.
The current template (actually not even a template) is meant to be deleted right after the document is created... Which makes create new document a little bit more complex than it should be.

Thanks

#62 我的环境

期望行为

yaml格式和properties格式的代码应该正常显示

当前行为

yaml出现错误

properties代码出现错误
<img width="867" alt="WX20191019-022128

As the project grows, it would be easier to contribute if the project follows a specific javascript style guide.
These are what I use in my personal projects:
Linter: https://github.com/eslint/eslint
Config: https://www.npmjs.com/package/eslint-config-airbnb

But any other would work too