fixed to image rake script

Gemfile

@@ -26,7 +26,7 @@ gem "meta_search", :git => "git://github.com/ernie/meta_search.git"
 gem "silent-postgres"
 gem "whenever", :require => false
 gem "sanitize", :git => "git://github.com/rgrove/sanitize.git"
-gem 'rmagick'
+gem 'rmagick', :require => "RMagick"
 
 group :development do
   gem 'pry'

lib/tasks/images.rake

@@ -1,3 +1,5 @@
+require 'danbooru_image_resizer/danbooru_image_resizer'
+
 namespace :images do
   desc "Generate medium-sized images of posts"
   task :generate_medium => :environment do