No need to define version of aws-sdk

[fixes #1977]

lib/paperclip/storage/s3.rb

@@ -4,7 +4,7 @@ module Paperclip
     # distribution. You can find out more about it at http://aws.amazon.com/s3
     # distribution. You can find out more about it at http://aws.amazon.com/s3
     #
     #
     # To use Paperclip with S3, include the +aws-sdk+ gem in your Gemfile:
     # To use Paperclip with S3, include the +aws-sdk+ gem in your Gemfile:
-    #   gem 'aws-sdk', '~> 1.6'
+    #   gem 'aws-sdk'
     # There are a few S3-specific options for has_attached_file:
     # There are a few S3-specific options for has_attached_file:
     # * +s3_credentials+: Takes a path, a File, a Hash or a Proc. The path (or File) must point
     # * +s3_credentials+: Takes a path, a File, a Hash or a Proc. The path (or File) must point
     #   to a YAML file containing the +access_key_id+ and +secret_access_key+ that Amazon
     #   to a YAML file containing the +access_key_id+ and +secret_access_key+ that Amazon