Capture variables above $9 misparsed

[moregan]

Perl-Critic/Perl-Critic#455
https://rt.cpan.org/Public/Bug/Display.html?id=72980

PPI does not recognize that the numbered capture variables can go higher than $9. E.g. for:

$_ = 'xxxxxxxxxxxxxxxxxxxx';
/(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)/;
my $x = $13;
print $x;

ppidump 'my $x = $13;'
                    PPI::Document
                      PPI::Statement::Variable
[    1,   1,   1 ]     PPI::Token::Word         'my'
[    1,   4,   4 ]     PPI::Token::Symbol       '$x'
[    1,   7,   7 ]     PPI::Token::Operator     '='
[    1,   9,   9 ]     PPI::Token::Magic        '$1'
[    1,  11,  11 ]     PPI::Token::Number       '3'
[    1,  12,  12 ]     PPI::Token::Structure    ';'