devel/aws-c-s3: Update to 1.2.0

Rename the PLIST_SUB variables to match devel/aws-c-common, which
upstream derives from the VERSION file as MAJOR.MINOR.PATCH and
MAJOR.MINOR.

ChangeLog: https://github.com/awslabs/aws-c-s3/releases/tag/v1.2.0

		https://github.com/awslabs/aws-c-s3/releases/tag/v1.1.3