Fix spelling error in manpage.

--- a/lib/Test/Reporter/Transport/File.pm
+++ b/lib/Test/Reporter/Transport/File.pm
@@ -62,7 +62,7 @@
 
     $report->transport_args( $dir );
 
-This transport class must have a writeable directory as its argument.
+This transport class must have a writable directory as its argument.
 
 =head1 METHODS
 
