Log Message:
Update RMagick to 2.7.1.

RMagick 2.7.1
    o Fix bug #22471, Magick::fonts can abend on 64-bit systems (bug report and
      patch by James Le Cuirot)
    o ImageList.new accepts a block which is passed on to Image::read when
      reading the input  images. The block is executed in the context of an
      Image::Info object.
    o Add support for the "user" image property.
    o Define the Magick::FatalImageMagickError exception class, raised if
      ImageMagick raises a fatal (unrecoverable) exception.
    o Added feature #22618, Image#total_ink_density (request by F. Behrens)