Update README.md

Links should be secure

Author: f3ath

README.md

@@ -92,7 +92,7 @@ Defines the logic for constructing and matching URLs for resources, collections
 The URL construction is used by both the Client (See [RoutingClient] for instance) and the Server libraries.
 The [StandardRouting] implements the [Recommended URL design].
 
-[JSON:API]: http://jsonapi.org
+[JSON:API]: https://jsonapi.org
 [Sparse fieldsets]: https://jsonapi.org/format/#fetching-sparse-fieldsets
 [Inclusion of Related Resources]: https://jsonapi.org/format/#fetching-includes
 [Collection Pagination]: https://jsonapi.org/format/#fetching-pagination
@@ -139,4 +139,4 @@ The [StandardRouting] implements the [Recommended URL design].
 
 
 [RouteFactory]: https://pub.dev/documentation/json_api/latest/routing/RouteFactory-class.html
-[StandardRouting]: https://pub.dev/documentation/json_api/latest/routing/StandardRouting-class.html
+[StandardRouting]: https://pub.dev/documentation/json_api/latest/routing/StandardRouting-class.html