Log Message:
Update ruby-prawn to 2.1.0.

PrawnPDF 2.1.0 – 2016-02-29

Added support for PNG images with indexed transparency

  Prawn now properly hadles transparency in PNG images with indexed color.

  (Maciej Mucha, #783; Alexander Mankuta, #920)

Prawn no longer generates IRB warnings

  Fix a few issues with code style that were triggering warnings in
  IRB when run in verbose mode (irb -w).

  (Jesse Doyle, #914)

Gradients applied inside transformations are now correctly positioned

  PDF gradients/patterns take coordinates in the coordinate space of
  the document, not the “user space”, so if you performed a
  scale/rotate/translate and then painted a gradient inside, it wasn't
  correctly positioned.

  This change tracks transformations applied to the document, and
  multiplies the gradient matrix with this tracked transformation
  matrix so that the gradient appears in the correct place in the
  document.

  Because this changes how the x and y coordinates are interpreted,
  you must manually add apply_transformations: true to your
  stroke_gradient and fill_gradient calls to use the fixed behaviour
  in Prawn 2. It is expected that this will be the default in Prawn 3.

  Please refer to the wiki page on this change for more information.

  (Roger Nesbitt, #891, #894)

Prawn::Graphics::BlendMode#blend_mode added

  Blend modes can be used to change the way two layers are blended
  together. The BM key is added to the External Graphics State based
  on the v1.4 PDF spec. blend_mode accepts a single blend mode or
  array of blend modes. If an array is passed, the PDF viewer blends
  layers based on the first valid blend mode.