README.md: Update site URL

README.md

@@ -7,4 +7,4 @@ gorilla/context is a general purpose registry for global request variables.
 > Note: gorilla/context, having been born well before `context.Context` existed, does not play well
 > with the shallow copying of the request that [`http.Request.WithContext`](https://golang.org/pkg/net/http/#Request.WithContext) (added to net/http Go 1.7 onwards) performs. You should either use *just* gorilla/context, or moving forward, the new `http.Request.Context()`.
 
-Read the full documentation here: http://www.gorillatoolkit.org/pkg/context
+Read the full documentation here: https://www.gorillatoolkit.org/pkg/context