doc: Fix typo in logical decoding documentation
doc: Fix typo in logical decoding documentation

From: Petr Jelinek <c327e92ea10f7773037429ba850de356a617881c@2ndquadrant.com>

zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl