Move the build badge to the badge list (#5060)

Move the `build` badge to the badge list.
Signed-off-by: zhulongcheng <zhulongcheng.me@gmail.com>

README.md

-# Prometheus [![Build Status](https://travis-ci.org/prometheus/prometheus.svg)][travis]
+# Prometheus 
 
+[![Build Status](https://travis-ci.org/prometheus/prometheus.svg)][travis]
 [![CircleCI](https://circleci.com/gh/prometheus/prometheus/tree/master.svg?style=shield)][circleci]
 [![Docker Repository on Quay](https://quay.io/repository/prometheus/prometheus/status)][quay]
 [![Docker Pulls](https://img.shields.io/docker/pulls/prom/prometheus.svg?maxAge=604800)][hub]