message: docs: fix loading demo bug
diff: @@ -2,6 +2,7 @@ import React from 'react'
  import DocViewer from '../../../libs/doc-viewer'
  import Button from '../../../components/button'
  import Panel from '../../../components/panel'
  +import Loading from '../../../components/loading'
  const prefix = 'loading-api'
  const code = `
  import React from 'react'
  @@ -53,7 +54,7 @@ class Demo extends React.Component {
  const DemoApi = () => (
  <DocViewer
  code={code}
  - scope={{ Button, Panel }}
  + scope={{ Button, Panel, Loading }}
  prefix={prefix}
  />
  )
  