Require Hash::Util
    
    Data::Dump::Streamer loads Hash::Util on recent perls in order to
    provide Data::Dump::Streamer::lock_ref_keys() implementation that
    uses Hash::Util::lock_keys().
    
    A failure to load Hash::Util is missed because the load is hidden in
    an eval argument for some other reasons. Then the tests fail in
    Data::Dump::Streamer::AUTOLOAD() on locating nonexistent lock_keys().
    
    I wanted to report it to the upstream but than I noticed, that Build.PL
    declares the dependency.