pgsql: doc: adjust "cities" example to be consistent with other SQL

doc: adjust "cities" example to be consistent with other SQL

Reported-by: tom@crystae.net

Discussion: /messages/by-id/162345756191.14472.9754568432103008703@wrigleys.postgresql.org

Backpatch-through: 9.6

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6cfa2f99013adf23953278f4feb6916c59feb292

Modified Files
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doc/src/sgml/advanced.sgml | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)