code: func EnvVariableName(name string) Configurator {
  	return func(c *Config) {
  		c.shouldUpdate = func() bool {
  			return envVariableSet(name)
  		}
  	}
  }
docs: // EnvVariableName can be used to customize the environment variable that determines whether snapshots
  // should be updated e.g.
  //  cupaloy.New(EnvVariableName("UPDATE"))
  // Will create an instance where snapshots will be updated if the UPDATE environment variable is set.
  // Default: UPDATE_SNAPSHOTS