Double jump FPS Controller

If in air i press space,when i land jump again.Or if i press space 2 times .How to fix it?

Change it on the FPSController.cs!

 void Update () {
       ...
       if (!m_Jump) {
          m_Jump = CrossPlatformInputManager.GetButtonDown ("Jump");
       }
       ...
    }

to

if (!m_Jump) {
   if (m_CharacterController.isGrounded) {   
      m_Jump = CrossPlatformInputManager.GetButtonDown ("Jump");
   }
}