Skip imagemagick tests on Travis.

spec/models/optimized_image_spec.rb

@@ -4,6 +4,7 @@ describe OptimizedImage do
   let(:upload) { build(:upload) }
   before { upload.id = 42 }
 
+  unless ENV["TRAVIS"]
     describe '.crop' do
       it 'should work correctly' do
         tmp_path = "/tmp/cropped.png"
@@ -65,6 +66,7 @@ describe OptimizedImage do
         end
       end
     end
+  end
 
   describe ".safe_path?" do