Implement code_change/3 for our GenServers

lib/nostrum/shard/connector.ex

@@ -39,4 +39,8 @@ defmodule Nostrum.Shard.Connector do
     Process.sleep(@wait_time - time)
     {:reply, :ok, %{state | last_connect: Util.now()}}
   end
+
+  def code_change(_version, state, _extra) do
+    {:ok, state}
+  end
 end

lib/nostrum/voice.ex

@@ -773,6 +773,11 @@ defmodule Nostrum.Voice do
     {:noreply, Map.delete(state, guild_id)}
   end
 
+  @doc false
+  def code_change(_version, state, data, _extra) do
+    {:ok, state, data}
+  end
+
   @doc false
   def start_if_ready(%VoiceState{} = voice) do
     if VoiceState.ready_for_ws?(voice) do

lib/nostrum/voice/ports.ex

@@ -160,4 +160,8 @@ defmodule Nostrum.Voice.Ports do
   def handle_info(_, state) do
     {:noreply, state}
   end
+
+  def code_change(_version, state, data, _extra) do
+    {:ok, state, data}
+  end
 end

lib/nostrum/voice/session.ex

@@ -214,6 +214,10 @@ defmodule Nostrum.Voice.Session do
     :gun.close(state.conn)
   end
 
+  def code_change(_old_vsn, state, _extra) do
+    {:ok, state}
+  end
+
   def restart_session_async(state) do
     spawn(fn ->
       Process.monitor(state.conn_pid)