Fix typo in TAP tests of pg_receivewal

Introduced in d62bcc8, noticed while hacking in the area.

Author: michaelpq

src/bin/pg_basebackup/t/020_pg_receivewal.pl

@@ -39,7 +39,7 @@
 		'--compress',    '1'
 	],
 	qr/\Qpg_receivewal: error: cannot use --compress with --compression-method=none/,
-	'failure if --compress spwcified with --compression-method=none');
+	'failure if --compress specified with --compression-method=none');
 
 # Slot creation and drop
 my $slot_name = 'test';