parser: Fix port name typo.

* gash/parser.scm (read-sh): Read from 'current-input-port' instead
of 'current-output-port'.

gash/parser.scm

@@ -824,7 +824,7 @@ port if @var{port} is unspecified)."
   (define stop? #f)
   (define (stop!) (set! stop? #t))
 
-  (let* ((port (or port (current-output-port))))
+  (let* ((port (or port (current-input-port))))
     (parse port #:lex-hook (lambda (lex) (if stop? '*eoi* (lex)))
            #:command-hook stop!)))