add imagemagick buildpack

.buildpacks

@@ -1,2 +1,3 @@
 https://github.com/gregburek/heroku-buildpack-pgbouncer.git#v0.3.3
+https://github.com/mcollina/heroku-buildpack-imagemagick
 https://github.com/heroku/heroku-buildpack-ruby.git

Procfile

@@ -1,2 +1,2 @@
 web: bin/start-pgbouncer-stunnel bundle exec puma --port $PORT --threads ${PUMA_MIN_THREADS:-0}:${PUMA_MAX_THREADS:-4} --workers ${PUMA_WORKERS:-1} --environment ${RACK_ENV:-development} --quiet
-worker: bin/bundle exec sidekiq -c 4
+worker: bin/bundle exec sidekiq -c 3

app/models/image.rb

@@ -2,10 +2,13 @@ class Image < ActiveRecord::Base
   has_many :favorites
   has_many :passes
 
-  has_attached_file :file, path: ":shortcode.:extension"
+  has_attached_file :file, path: ":shortcode.:extension", styles: {
+    thumb: ["300x300", :png]
+  }
   validates_attachment :file, content_type: { content_type: 'image/gif' }
   has_attached_file :mp4, path: ':shortcode.:extension'
   validates_attachment :mp4, content_type: { content_type: 'video/mp4' }
+
   validates :original_source, uniqueness: true
   validates :file_fingerprint, uniqueness: { allow_blank: true }