Fix ImageMagick incompatibility on CI

.github/workflows/deploy.yml

@@ -35,11 +35,6 @@ jobs:
           KEY: ${{ github.workspace }}/secret.key
         run: cd bin/dither && bundle exec ruby dither.rb >> dither.log 2>&1 &
 
-      - name: Install ImageMagick
-        run: |
-          sudo apt update
-          sudo apt install imagemagick
-
       - name: Test build
         env:
           DITHER_SERVER: http://localhost:4567

.gitignore

@@ -2,3 +2,4 @@
 public
 resources/_gen
 secret.key
+bin/dither/tmp

bin/dither/dither.rb

@@ -25,15 +25,15 @@ get "/*" do |path|
       -iter 1000000
   )
 
-  MiniMagick::Tool::Magick.new do |magick|
+  convert = MiniMagick::Tool::Convert.new
-    magick << @decrypted.path
+  convert << @decrypted.path
-    magick.resize "#{geometry}^"
+  convert.resize "#{geometry}^"
-    magick.gravity "center"
+  convert.gravity "center"
-    magick.extent geometry
+  convert.extent geometry
-    magick.ordered_dither "o8x8"
+  convert.ordered_dither "o8x8"
-    magick.monochrome
+  convert.monochrome
-    magick << @dithered.path
+  convert << @dithered.path
-  end
+  convert.call
 
   content_type "image/png"
   File.open(@dithered.path)