use XML::Twig;

my $twig= XML::Twig->new(
        pretty_print => 'indented',
        twig_handlers => {
            jdk => sub{ 
            $_->set_text( 'JDK 1.8.0_40' )
            },
            },
        );
$twig->parsefile_inplace( 'nightly.xml', 'bak.*' );
$twig->flush;

##</code><code>##

<jdk>JDK 1.7.0_40</jdk>