enabled the 'smartmatch' experimental feature

smartmatch is considered experimental since perl 5.18 (see [changelog] (http://perldoc.perl.org/perl5180delta.html#The-smartmatch-family-of-features-are-now-experimental))

Compilation fails, when using a perl version greater than 5.18, because of `use warnings FATAL => 'all';`

Adding `use experimental 'smartmatch'` should fix the issue and should not break anything for older perl versions (see [A little nicer way to use smartmatch on perl 5.18] (http://blogs.perl.org/users/mike_b/2013/06/a-little-nicer-way-to-use-smartmatch-on-perl-518.html))