Add missing serial commas

doc/src/sgml/ref/pgbench.sgml

@@ -636,7 +636,7 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
        <para>
         Report the following statistics for each command after the benchmark
         finishes: the average per-statement latency (execution time from the
-        perspective of the client), the number of failures and the number of
+        perspective of the client), the number of failures, and the number of
         retries after serialization or deadlock errors in this command.  The
         report displays retry statistics only if the
         <option>--max-tries</option> option is not equal to 1.

src/bin/pgbench/pgbench.c

@@ -908,7 +908,7 @@ usage(void)
 		   "                           protocol for submitting queries (default: simple)\n"
 		   "  -n, --no-vacuum          do not run VACUUM before tests\n"
 		   "  -P, --progress=NUM       show thread progress report every NUM seconds\n"
-		   "  -r, --report-per-command report latencies, failures and retries per command\n"
+		   "  -r, --report-per-command report latencies, failures, and retries per command\n"
 		   "  -R, --rate=NUM           target rate in transactions per second\n"
 		   "  -s, --scale=NUM          report this scale factor in output\n"
 		   "  -t, --transactions=NUM   number of transactions each client runs (default: 10)\n"