Even though AWS::AppSync::FunctionConfiguration type was added recently, it's still missing the related aws cloudformation package support, similarly to other AWS::AppSync:: resources.
aws --version
aws-cli/1.16.81 Python/2.7.15 Darwin/17.7.0 botocore/1.12.71
Even though
AWS::AppSync::FunctionConfigurationtype was added recently, it's still missing the relatedaws cloudformation packagesupport, similarly to otherAWS::AppSync::resources.aws --version