pgsql: doc: Fix some grammar and inconsistencies

doc: Fix some grammar and inconsistencies

Some comments are fixed while on it.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20200818171702.GK17022@telsasoft.com
Backpatch-through: 9.6

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b3d89b7a889614a5ad549bae49b8a6fdda3a6bdd

Modified Files
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doc/src/sgml/logicaldecoding.sgml          | 2 +-
doc/src/sgml/ref/alter_table.sgml          | 2 +-
doc/src/sgml/ref/create_subscription.sgml  | 2 +-
doc/src/sgml/ref/pg_verifybackup.sgml      | 7 ++++---
doc/src/sgml/sources.sgml                  | 2 +-
src/backend/replication/logical/relation.c | 4 ++--
src/backend/storage/lmgr/proc.c            | 2 +-
7 files changed, 11 insertions(+), 10 deletions(-)