Make AwsS3Resolver compatible with SDK v3

[cdaguerre]

AwsS3Resolver is not compatible with AWS SDK v3 released earlier today because Enum constants were removed (refer: http://docs.aws.amazon.com/aws-sdk-php/v3/guide/guide/migration.html#enum-classes-have-been-removed)

This simple commit should make the resolver compatible with v3.

[lsmith77]

looks good to me .. @makasim ?

[lsmith77]

BTW I guess this line should also be updated then to include v3:
https://github.com/liip/LiipImagineBundle/blob/master/composer.json#L45

[cdaguerre]

@lsmith77 composer.json updated.

[lsmith77]

thx

[makasim]

require-dev rely on 2.4 version of SDK, not sure we have to keep it or update it, any thoughts?

[cdaguerre]

@makasim Actually I wasn't sure either.

I updated aws/aws-sdk-php to v3 locally and ran the unit test suite (excluding functional). I only got a bunch of symfony deprecation warnings due to the new version of the debug component, so I guess it works as expected and as it used to with v2.

According to the AWS migration guide:

• Given the _"data-driven and API version agnostic nature of Version 3"_, I guess this means from v3.0 on, the resolver should work with any new release and API version.
• They also state they will follow strict SemVer standards from now on.

So my guess is: If it works with v2 and there should be no BC breaks going forward (at least in the v3.0 branch), we might aswell update the composer requirement.