Update devstack.template

I get this error when I try to deploy this template: Property error : devstack_server: user_data The Parameter (enable_heat) was not provided.

I added this piece back in: (It works fine with this)
enable_heat:
    default: "false"
    description: Enable the Heat service in Devstack
    type: string
    constraints:
    - allowed_values: ["true", "false"]
      description: must be either "true" or "false"