ruby-vips: Vips::Error: vipspng: out of order read at line 352

getting png error on ruby-vips 1.0.5

DragonflyLibvips::Processors::Thumb::format#test_0001_changes the format if passed in:
Vips::Error: vipspng: out of order read at line 352
    /home/travis/.rvm/gems/ruby-2.2.5/gems/ruby-vips-1.0.5/lib/vips/call.rb:186:in `build'
    /home/travis/.rvm/gems/ruby-2.2.5/gems/ruby-vips-1.0.5/lib/vips/call.rb:253:in `invoke'
    /home/travis/.rvm/gems/ruby-2.2.5/gems/ruby-vips-1.0.5/lib/vips/call.rb:282:in `call_base'
    /home/travis/.rvm/gems/ruby-2.2.5/gems/ruby-vips-1.0.5/lib/vips/image.rb:670:in `write_to_buffer'
    /home/travis/build/tomasc/dragonfly_libvips/lib/dragonfly_libvips/processors/thumb.rb:40:in `call'
    /home/travis/build/tomasc/dragonfly_libvips/test/dragonfly_libvips/processors/thumb_test.rb:69:in `block (3 levels) in <top (required)>'

the test output: https://travis-ci.org/tomasc/dragonfly_libvips

the source code in Ruby: https://github.com/tomasc/dragonfly_libvips/blob/thumbnail/lib/dragonfly_libvips/processors/thumb.rb#L38-L40

the image: https://github.com/tomasc/dragonfly_libvips/blob/thumbnail/samples/beach.png

this happens both on my machine (OS X) as well as on Travis CI - both libvips 8.5.5

@jcupitt perhaps I am missing some libs?