Fix broken link

Closes gh-16666

Author: Tetsuya3850

spring-boot-docs/src/main/asciidoc/index.adoc

@@ -35,7 +35,7 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :dependency-management-plugin: https://github.com/spring-gradle-plugins/dependency-management-plugin
 :dependency-management-plugin-documentation: {dependency-management-plugin}/blob/master/README.md
 :spring-boot-maven-plugin-site: https://docs.spring.io/spring-boot/docs/{spring-boot-docs-version}/maven-plugin
-:spring-initializr-reference: https://docs.spring.io/initializr/docs/current/reference/htmlsingle
+:spring-initializr-reference: https://docs.spring.io/initializr/docs/current/reference/html
 :spring-reference: https://docs.spring.io/spring/docs/{spring-docs-version}/spring-framework-reference/htmlsingle
 :spring-security-reference: https://docs.spring.io/spring-security/site/docs/{spring-security-docs-version}/reference/htmlsingle
 :spring-security-oauth2-reference: https://projects.spring.io/spring-security-oauth/docs/oauth2.html