Update spec to use expect syntax

Author: jonmagic

spec/lib/grim/image_magick_processor_spec.rb

@@ -26,7 +26,7 @@
     end
 
     it "should return page count" do
-      @processor.count(fixture_path("smoker.pdf")).should == 25
+      expect(@processor.count(fixture_path("smoker.pdf"))).to eq(25)
     end
   end