Log Message:
Update ruby-mini-magick to 4.1.0.

4.1.0

* Added MiniMagick::Tool#stack for building ImageMagick stacks:

	MiniMagick::Tool::Convert.new do |convert|
	  convert << "wand.gif"
	  convert.stack do |stack|
	    stack << "wand.gif"
	    stack.rotate(30)
	  end
	  convert << "images.gif"
	end

	convert wand.gif \( wand.gif -rotate 90 \) images.gif

4.0.4

* Allow filenames with colon in their names (thanks to @agorf)