Provide meaningful information when incorrect webhook link provided

[sergii4]

If you provide incorrect link in

func NewWebhookWithCert(link string, file interface{}) WebhookConfig {
     u, _ := url.Parse(link)
    ...
}

you have no chance to understand what have you done wrong, because error is not checked.
I propose to invoke log.Fatal(err) or log.Fatalf("link format is incorrect %s, err)