Fix typo

Author: Daniel Westermann
Backpatch-through: 9.6
Discussion: https://postgr.es/m/GV0P278MB0483A7AA85BAFCC06D90F453D2739@GV0P278MB0483.CHEP278.PROD.OUTLOOK.COM

src/backend/utils/misc/guc.c

@@ -1320,7 +1320,7 @@ static struct config_bool ConfigureNamesBool[] =
 
 	{
 		{"wal_log_hints", PGC_POSTMASTER, WAL_SETTINGS,
-			gettext_noop("Writes full pages to WAL when first modified after a checkpoint, even for a non-critical modifications."),
+			gettext_noop("Writes full pages to WAL when first modified after a checkpoint, even for a non-critical modification."),
 			NULL
 		},
 		&wal_log_hints,