Correct the names of pgstattuple_approx output columns in the doc.
Correct the names of pgstattuple_approx output columns in the doc.

ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,adam8157/gpdb,oberstet/postgres-xl,50wu/gpdb,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,yazun/postgres-xl,50wu/gpdb,adam8157/gpdb,Postgres-XL/Postgres-XL,yazun/postgres-xl,50wu/gpdb,xinzweb/gpdb,oberstet/postgres-xl,techdragon/Postgres-XL,ovr/postgres-xl,jmcatamney/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,greenplum-db/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,ovr/postgres-xl,yazun/postgres-xl,xinzweb/gpdb,Postgres-XL/Postgres-XL,yazun/postgres-xl,zeroae/postgres-xl,techdragon/Postgres-XL,zeroae/postgres-xl,techdragon/Postgres-XL,adam8157/gpdb,50wu/gpdb,lisakowen/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,greenplum-db/gpdb,zeroae/postgres-xl,lisakowen/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,ashwinstar/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,ovr/postgres-xl,ashwinstar/gpdb,jmcatamney/gpdb,techdragon/Postgres-XL,adam8157/gpdb,50wu/gpdb,ovr/postgres-xl,adam8157/gpdb,zeroae/postgres-xl,yazun/postgres-xl,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,lisakowen/gpdb