SpringBoot Fix duplicate slashes in URL links

Fix links which have duplicate slashes in reference documentation.

link examples * https://docs.spring.io/spring-boot/docs/2.3.0.BUILD-SNAPSHOT/api//org/springframework/boot/SpringApplication.html * https://docs.oracle.com/javase/8/docs/api//java/time/Duration.html#parse-java.lang.CharSequence- * https://docs.spring.io/initializr/docs/current/reference/html//#user-guide * ...

Comment From: jkatada

@snicoll Thanks for the feedback. I've updated the PR. Please review.

Comment From: snicoll

@jkatada thanks for the follow-up and for making your first contribution to Spring Boot.