[gatsby-remark-code-repls] Fix validation error saying default template isn't importing React

[Swizec]

After a clean install of latest Gatsby I was getting this error

The page component at "node_modules/gatsby-remark-code-repls/default-redirect-template.js" didn't pass validation

You must import React at the top of the file for a React component to be valid

Add the following to the top of the component:

    import React from 'react'


The page component must export a React component for it to be valid

This PR fixes it.

I'm not sure if that signifies a deeper problem with whatever is doing the validation, but that's beyond my understanding. This was easier to get operational quick :)

[gatsbybot]

Deploy preview for gatsbygram ready!

Built with commit 4c05c09

https://deploy-preview-3974--gatsbygram.netlify.com

[KyleAMathews]

You must have caught the brief window when this bug was in existence yesterday :-)

I fixed it in #3949

Upgrade gatsby and you should be sorted! Thanks!