Fix runtime error on v.client.Do()
Fix runtime error on v.client.Do()

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x96f422]

When we handle webhooks from viber, we create instance by this way:

v := &viber.Viber{
		AppKey: token,
		Sender: viber.Sender{
			Name:   "MyPage",
			Avatar: "https://mysite.com/img/avatar.jpg",
		},
		//Message:   msgReceivedFunc,
		//Delivered: deliveredFunc,
	}
May be this is bad way, and we need to use .New() method everywhere, beause

v.client is nil. 

My fix: just check and init &http.Client{} if client is nil.
mileusna/viber