Use snake case in the configuration file

.lumerc.sample

@@ -1 +1 @@
-AccessToken = "token"
+access_token = "token"

cmd/command.go

@@ -9,7 +9,7 @@ import (
 )
 
 type Config struct {
-	AccessToken string
+	AccessToken string               `toml:"access_token"`
 	Colors      map[string][]float32 `toml:"colors"`
 }