gnu: services: nginx: Fix key verification.

* gnu/services/web.scm (default-nginx-server-config): Fix wrong variable name.

gnu/services/web.scm

@@ -162,7 +162,7 @@ (define (default-nginx-server-config server)
        "")
    (if (nginx-server-configuration-ssl-certificate-key server)
        (let ((key (nginx-server-configuration-ssl-certificate-key server)))
-         (lstat certificate)
+         (lstat key)
          (string-append "      ssl_certificate_key " key ";\n"))
        "")
    "      root " (nginx-server-configuration-root server) ";\n"