Remove extra / from artifactory server param

Fixes gh-13535

ci/parameters.yml

@@ -4,7 +4,7 @@ email-to: ["spring-boot-dev@pivotal.io"]
 github-repo: "https://github.com/spring-projects/spring-boot.git"
 github-repo-name: "spring-projects/spring-boot"
 docker-hub-organization: "springci"
-artifactory-server: "https://repo.spring.io/"
+artifactory-server: "https://repo.spring.io"
 branch: "2.0.x"
 build-name: "spring-boot"
 pipeline-name: "spring-boot-2.0.x"