fixing the broken concourse badge in README (#5120)

README.md

-**Concourse Pipeline** [![Concourse Build Status](https://gpdb.data.pivotal.ci/api/v1/teams/gpdb/pipelines/gpdb_master/jobs/gpdb_rc_packaging_centos/badge)](https://gpdb.data.pivotal.ci/teams/gpdb) |
+**Concourse Pipeline** [![Concourse Build Status](https://gpdb.bosh.pivotalci.info/api/v1/teams/main/pipelines/gpdb_master/badge)](https://gpdb.data.pivotal.ci/teams/gpdb) |
 **Travis Build** [![Travis Build Status](https://travis-ci.org/greenplum-db/gpdb.svg?branch=master)](https://travis-ci.org/greenplum-db/gpdb)
 
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