Fix typo in README
Fix typo in README

Author: Daniel Gustafsson <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@yesql.se>

greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb