I keep getting a message that bareword “is_perl55” is not allowed when “strict subs” is used.

You should post the full message. It surely sports a file name and line number. If it doesn't, try

use Carp;
BEGIN { $SIG{__DIE__} = \&Carp::confess; }
use WWW::Mechanize;
[download]

which should give you a clue.