add missing API key message localization (en_en & nb_no)

localization/en_en/music.yaml

@@ -85,3 +85,4 @@ errors:
   right_channel: You need to be in the right voice channel
   my_channel: You need to be in my voicechannel
   full_channel: The channel is currently full
+  missing_api_key: API key is missing

localization/nb_no/music.yaml

@@ -85,3 +85,4 @@ errors:
   right_channel: Du må være i riktig kanal
   my_channel: Du må være i samme stemmekanal som meg
   full_channel: Den kanalen er full
+  missing_api_key: API-nøkkel mangler