Bug#839886: update $& performance hit wording

[積丹尼 Dan Jacobson]

Package: perl-doc
Version: 5.24.1~rc3-3
Severity: wishlist
File: /usr/share/man/man1/perlvar.1.gz

Since you say

       In Perl 5.20.0 a new copy-on-write system was enabled by default, which
       finally fixes all performance issues with these three variables, and
       makes them safe to use anywhere.

Then perhaps don't still say

           print $`, $&, $'; # bad: perfomance hit

           print             # good: no perfomance hit


above it.