Update aws-sdk development dependency

Paperclip 5 no longer supports aws-sdk v1. Having a lot of constraints
in one gem dependency caused issues when pushing the gem (ref:
https://github.com/rubygems/rubygems/issues/1564).

This commit simplifies the dependency restriction to `>= 2.0.33`.

paperclip.gemspec

@@ -35,7 +35,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency('rspec', '~> 3.0')
   s.add_development_dependency('appraisal')
   s.add_development_dependency('mocha')
-  s.add_development_dependency('aws-sdk', '>= 1.5.7', "< 3.0", *((0..33).to_a.collect{ |release_number| "!= 2.0.#{release_number}" }))
+  s.add_development_dependency('aws-sdk', '>= 2.0.33', '< 3.0')
   s.add_development_dependency('bourne')
   s.add_development_dependency('cucumber', '~> 1.3.18')
   s.add_development_dependency('aruba', '~> 0.9.0')