code: public function setEnvironment($environment)
  	{
  		if ($this->booting) {
  			throw new \RuntimeException('Cannot set environment after application has booted');
  		}
  
  		if ($environment instanceof Closure) {
  			$environment = call_user_func($environment);
  		}
  
  		if (!is_string($environment)) {
  			throw new \InvalidArgumentException('Environment must be a string');
  		}
  
  		$this->environment = $environment;
  	}
docs: Set the environment of the application. Has to be called before boot().
  
  @param string $environment