fix: remove config file fd leak

I don't know why I didn't just close it after leaving the function.
There is no other use of the fd...

config.go

@@ -18,6 +18,7 @@ func readConfig() (*config, error) {
  if err != nil {
  return nil, err
  }
+ defer open.Close()
 
  d := yaml.NewDecoder(open)
  d.KnownFields(true)