Fix env variable used for API token (GitbookIO#241)

Author: SamyPesse

src/middleware.ts

@@ -106,7 +106,7 @@ export async function middleware(request: NextRequest) {
  const resolved = await withAPI(
  new GitBookAPI({
  endpoint: apiEndpoint,
- authToken: process.env.GITBOOK_API_TOKEN,
+ authToken: process.env.GITBOOK_TOKEN,
  userAgent: userAgent(),
  }),
  () => lookupSpaceForURL(mode, request, inputURL),