docs/data-source/aws_lambda_invocation: Add information about jsondecode() in Terraform 0.12
docs/data-source/aws_lambda_invocation: Add information about jsondecode() in Terraform 0.12

Reference: https://github.com/terraform-providers/terraform-provider-aws/issues/9184

kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws