Merge pull request spring-projects#19008 from Christoph Dreis

* pr/19008:
  Fix build badge in README

Closes spring-projectsgh-19008

Author: mbhave

README.adoc

@@ -1,4 +1,4 @@
-= Spring Boot image:https://ci.spring.io/api/v1/teams/spring-boot/pipelines/spring-boot/jobs/build/badge["Build Status", link="https://ci.spring.io/teams/spring-boot/pipelines/spring-boot?groups=Build"] image:https://badges.gitter.im/Join Chat.svg["Chat",link="https://gitter.im/spring-projects/spring-boot?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge"]
+= Spring Boot image:https://ci.spring.io/api/v1/teams/spring-boot/pipelines/spring-boot-2.1.x/jobs/build/badge["Build Status", link="https://ci.spring.io/teams/spring-boot/pipelines/spring-boot-2.1.x?groups=Build"] image:https://badges.gitter.im/Join Chat.svg["Chat",link="https://gitter.im/spring-projects/spring-boot?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge"]
 :docs: https://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference
 
 Spring Boot makes it easy to create Spring-powered, production-grade applications and