It looks like [either could be correct](https://en.wikipedia.org/wiki/HTTP_referer), but one spelling is used [in the source](https://github.com/gocolly/colly/blob/389bc3c811e16f7bfba497d8dc6bf4f98a51c8fe/extensions/referer.go#L10) and another [on the site](https://github.com/gocolly/site/blob/f8176a52a36b6ef82692fa7b4a5bacfb21cfdf75/content/docs/best_practices/extensions.md). I assume the code would be the one to keep, and the site the one to change.
It looks like either could be correct, but one spelling is used in the source and another on the site.
I assume the code would be the one to keep, and the site the one to change.