0.60.0: [tfstate-backend] Update to 0.7.0

Update to terraform-aws-tfstate-backend version 0.7.0 (#145)

Note that this creates an S3 bucket that requires encrypted uploads, but does not specify encrypted uploads in the backend configuration, for backwards compatibility. You may need to set backend.encrypt=true somehow. You can do it on the command line by adding the option -backend-config=encrypt=true. If you are using Cloudposse's tfenv, you can do it by setting an environment variable: export TF_CLI_INIT_BACKEND_CONFIG_ENCRYPT=1 ("true" does not work, see cloudposse-archives/tfenv#10)