refactor: revise helloworld example

examples/helloworld/lib/helloworld.pb.ex

@@ -1,31 +1,25 @@
 defmodule Helloworld.HelloRequest do
-  use Protobuf
+  @moduledoc false
+  use Protobuf, protoc_gen_elixir_version: "0.10.0", syntax: :proto3
 
-  @type t :: %__MODULE__{
-          name: String.t()
-        }
-  defstruct [:name]
-
-  field :name, 1, optional: true, type: :string
+  field :name, 1, type: :string
 end
 
 defmodule Helloworld.HelloReply do
-  use Protobuf
-
-  @type t :: %__MODULE__{
-          message: String.t()
-        }
-  defstruct [:message]
+  @moduledoc false
+  use Protobuf, protoc_gen_elixir_version: "0.10.0", syntax: :proto3
 
-  field :message, 1, optional: true, type: :string
+  field :message, 1, type: :string
 end
 
 defmodule Helloworld.Greeter.Service do
-  use GRPC.Service, name: "helloworld.Greeter"
+  @moduledoc false
+  use GRPC.Service, name: "helloworld.Greeter", protoc_gen_elixir_version: "0.10.0"
 
   rpc :SayHello, Helloworld.HelloRequest, Helloworld.HelloReply
 end
 
 defmodule Helloworld.Greeter.Stub do
+  @moduledoc false
   use GRPC.Stub, service: Helloworld.Greeter.Service
 end

examples/helloworld/lib/helloworld_app.ex

@@ -2,10 +2,8 @@ defmodule HelloworldApp do
   use Application
 
   def start(_type, _args) do
-    import Supervisor.Spec
-
     children = [
-      supervisor(GRPC.Server.Supervisor, [{Helloworld.Endpoint, 50051}])
+      {GRPC.Server.Supervisor, {Helloworld.Endpoint, 50051}}
     ]
 
     opts = [strategy: :one_for_one, name: HelloworldApp]