changed aws-sdk dependency version for ActiveStorage support

[superchell]

fix dependencies conflict like this:

Bundler could not find compatible versions for gem "aws-sdk-core":
  In Gemfile:
    camaleon_cms was resolved to 2.4.5.10, which depends on
      aws-sdk (~> 2) was resolved to 2.0.1.pre, which depends on
        aws-sdk-resources (= 2.0.1.pre) was resolved to 2.0.1.pre, which depends on
          aws-sdk-core (= 2.0.1)

    aws-sdk-s3 was resolved to 1.0.0.rc5, which depends on
      aws-sdk-core (= 3.0.0.rc1)