Update cocaine dependency

Cocaine changes how it returns the supplied path in 0.5.5. While this
has no effect on the workings of Paperclip in a normal capacity, it does
break the tests. This change fixes that and updates the cocaine
dependency to 0.5.5.

paperclip.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
 
   s.add_dependency('activemodel', '>= 3.0.0')
   s.add_dependency('activesupport', '>= 3.0.0')
-  s.add_dependency('cocaine', '~> 0.5.3')
+  s.add_dependency('cocaine', '~> 0.5.5')
   s.add_dependency('mime-types')
 
   s.add_development_dependency('activerecord', '>= 3.0.0')

spec/paperclip/paperclip_spec.rb

@@ -20,7 +20,7 @@
     it "saves Cocaine::CommandLine.path that set before" do
       Cocaine::CommandLine.path = "/opt/my_app/bin"
       Paperclip.run("convert", "stuff")
-      assert_equal [Cocaine::CommandLine.path].flatten.include?("/opt/my_app/bin"), true
+      assert_equal Cocaine::CommandLine.path.include?("/opt/my_app/bin"), true
     end
 
     it "does not duplicate Cocaine::CommandLine.path on multiple runs" do