Update release notes for 8.1.3.
Update release notes for 8.1.3.

lpetrov-pivotal/gpdb,rubikloud/gpdb,lintzc/gpdb,ovr/postgres-xl,greenplum-db/gpdb,CraigHarris/gpdb,atris/gpdb,yazun/postgres-xl,randomtask1155/gpdb,Quikling/gpdb,tpostgres-projects/tPostgres,Quikling/gpdb,50wu/gpdb,ahachete/gpdb,randomtask1155/gpdb,ashwinstar/gpdb,zaksoup/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,ovr/postgres-xl,janebeckman/gpdb,techdragon/Postgres-XL,lisakowen/gpdb,cjcjameson/gpdb,foyzur/gpdb,cjcjameson/gpdb,ahachete/gpdb,ashwinstar/gpdb,chrishajas/gpdb,0x0FFF/gpdb,rubikloud/gpdb,janebeckman/gpdb,postmind-net/postgres-xl,cjcjameson/gpdb,50wu/gpdb,Chibin/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,ahachete/gpdb,xinzweb/gpdb,lisakowen/gpdb,janebeckman/gpdb,royc1/gpdb,janebeckman/gpdb,royc1/gpdb,0x0FFF/gpdb,yuanzhao/gpdb,janebeckman/gpdb,zeroae/postgres-xl,lintzc/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,adam8157/gpdb,pavanvd/postgres-xl,CraigHarris/gpdb,edespino/gpdb,xuegang/gpdb,Quikling/gpdb,lintzc/gpdb,jmcatamney/gpdb,xuegang/gpdb,xuegang/gpdb,techdragon/Postgres-XL,randomtask1155/gpdb,atris/gpdb,Chibin/gpdb,pavanvd/postgres-xl,rvs/gpdb,xuegang/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,yazun/postgres-xl,Chibin/gpdb,rubikloud/gpdb,yuanzhao/gpdb,zeroae/postgres-xl,randomtask1155/gpdb,zeroae/postgres-xl,rvs/gpdb,edespino/gpdb,royc1/gpdb,adam8157/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,edespino/gpdb,ahachete/gpdb,foyzur/gpdb,tangp3/gpdb,Postgres-XL/Postgres-XL,yuanzhao/gpdb,xinzweb/gpdb,zaksoup/gpdb,0x0FFF/gpdb,adam8157/gpdb,Chibin/gpdb,tangp3/gpdb,rvs/gpdb,cjcjameson/gpdb,Postgres-XL/Postgres-XL,snaga/postgres-xl,pavanvd/postgres-xl,chrishajas/gpdb,chrishajas/gpdb,kaknikhil/gpdb,xuegang/gpdb,xuegang/gpdb,rvs/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,zaksoup/gpdb,xuegang/gpdb,CraigHarris/gpdb,ahachete/gpdb,tpostgres-projects/tPostgres,xinzweb/gpdb,lintzc/gpdb,jmcatamney/gpdb,chrishajas/gpdb,foyzur/gpdb,adam8157/gpdb,royc1/gpdb,arcivanov/postgres-xl,zaksoup/gpdb,arcivanov/postgres-xl,yazun/postgres-xl,CraigHarris/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,50wu/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,postmind-net/postgres-xl,Quikling/gpdb,Quikling/gpdb,0x0FFF/gpdb,atris/gpdb,yazun/postgres-xl,ashwinstar/gpdb,0x0FFF/gpdb,rubikloud/gpdb,royc1/gpdb,snaga/postgres-xl,Chibin/gpdb,zaksoup/gpdb,tpostgres-projects/tPostgres,50wu/gpdb,Quikling/gpdb,lintzc/gpdb,techdragon/Postgres-XL,lintzc/gpdb,rvs/gpdb,lpetrov-pivotal/gpdb,tangp3/gpdb,postmind-net/postgres-xl,edespino/gpdb,lpetrov-pivotal/gpdb,ovr/postgres-xl,jmcatamney/gpdb,greenplum-db/gpdb,chrishajas/gpdb,oberstet/postgres-xl,rvs/gpdb,lisakowen/gpdb,jmcatamney/gpdb,foyzur/gpdb,jmcatamney/gpdb,randomtask1155/gpdb,oberstet/postgres-xl,zaksoup/gpdb,techdragon/Postgres-XL,royc1/gpdb,randomtask1155/gpdb,50wu/gpdb,lpetrov-pivotal/gpdb,kmjungersen/PostgresXL,yuanzhao/gpdb,yuanzhao/gpdb,ovr/postgres-xl,CraigHarris/gpdb,kaknikhil/gpdb,50wu/gpdb,rubikloud/gpdb,oberstet/postgres-xl,Quikling/gpdb,lisakowen/gpdb,edespino/gpdb,kmjungersen/PostgresXL,zeroae/postgres-xl,janebeckman/gpdb,greenplum-db/gpdb,foyzur/gpdb,lintzc/gpdb,jmcatamney/gpdb,snaga/postgres-xl,zaksoup/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,Chibin/gpdb,lpetrov-pivotal/gpdb,zeroae/postgres-xl,rvs/gpdb,Quikling/gpdb,postmind-net/postgres-xl,zaksoup/gpdb,tangp3/gpdb,edespino/gpdb,foyzur/gpdb,atris/gpdb,kmjungersen/PostgresXL,pavanvd/postgres-xl,arcivanov/postgres-xl,janebeckman/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,rvs/gpdb,lpetrov-pivotal/gpdb,cjcjameson/gpdb,ahachete/gpdb,arcivanov/postgres-xl,tangp3/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,edespino/gpdb,xinzweb/gpdb,xinzweb/gpdb,snaga/postgres-xl,greenplum-db/gpdb,snaga/postgres-xl,lintzc/gpdb,tangp3/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,atris/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,xinzweb/gpdb,tangp3/gpdb,Postgres-XL/Postgres-XL,rvs/gpdb,xuegang/gpdb,janebeckman/gpdb,ovr/postgres-xl,adam8157/gpdb,chrishajas/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,50wu/gpdb,Chibin/gpdb,kaknikhil/gpdb,xuegang/gpdb,Quikling/gpdb,CraigHarris/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,tangp3/gpdb,arcivanov/postgres-xl,edespino/gpdb,atris/gpdb,rubikloud/gpdb,ashwinstar/gpdb,adam8157/gpdb,cjcjameson/gpdb,xinzweb/gpdb,tpostgres-projects/tPostgres,ahachete/gpdb,Chibin/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,tpostgres-projects/tPostgres,Quikling/gpdb,yazun/postgres-xl,rubikloud/gpdb,techdragon/Postgres-XL,janebeckman/gpdb,kmjungersen/PostgresXL,rvs/gpdb,atris/gpdb,rubikloud/gpdb,edespino/gpdb,chrishajas/gpdb,Chibin/gpdb,greenplum-db/gpdb,50wu/gpdb,postmind-net/postgres-xl,lisakowen/gpdb,Chibin/gpdb,royc1/gpdb,edespino/gpdb,lintzc/gpdb,randomtask1155/gpdb,randomtask1155/gpdb,janebeckman/gpdb,foyzur/gpdb,xinzweb/gpdb,arcivanov/postgres-xl,lpetrov-pivotal/gpdb,atris/gpdb,adam8157/gpdb,foyzur/gpdb,cjcjameson/gpdb,adam8157/gpdb,kmjungersen/PostgresXL,oberstet/postgres-xl,yuanzhao/gpdb,royc1/gpdb,chrishajas/gpdb,ahachete/gpdb,0x0FFF/gpdb,lisakowen/gpdb