Update Test::Nginx link to point to current version.

Author: GUI

README.md

@@ -291,7 +291,7 @@ After checking out the repo, Docker can be used to run the test suite:
 $ docker-compose run app make test
 ```
 
-The test suite is implemented using nginx' [`Test::Nginx`](http://search.cpan.org/~agent/Test-Nginx-0.24/lib/Test/Nginx/Socket.pm) cpan module.
+The test suite is implemented using nginx' [`Test::Nginx`](https://metacpan.org/pod/Test::Nginx::Socket) cpan module.
 
 ## Credits