Revert "Update README with version requirement for aws-sdk"

v4.3.2 is a different tree than `master`, which is now targeting v5.
Thank you both for this commit and merge, but I'll revert it: paperclip
v4.3.2 doesn't include AWS v2 support.

This reverts commit 9b33fc0a.

[ci skip]

README.md

@@ -582,7 +582,7 @@ You may also choose to store your files using Amazon's S3 service. To do so, inc
 the `aws-sdk` gem in your Gemfile:
 
 ```ruby
-gem 'aws-sdk', '>= 2.0.0' # If using paperclip >= v.4.3.2
+gem 'aws-sdk', '>= 2.0.0' # If using paperclip `master` (upcoming v5.0)
 ```
 or
 ```ruby