closes #77 - add `web_url` field to `Issue` (#79)

* closes #77 - adds `web_url` field to `Issue`

* Add new fields in Issue struct to bring it up-to-date with Gitlab API

The following fields have been added to `Issue` struct
* `Subscribed`
* `UserNotesCount`
* `Confidential`
* `DueDate`
* `WebURL`

issues.go

@@ -70,6 +70,11 @@ type Issue struct {
 	State          string     `json:"state"`
 	UpdatedAt      *time.Time `json:"updated_at"`
 	CreatedAt      *time.Time `json:"created_at"`
+	Subscribed     bool       `json:"subscribed"`
+	UserNotesCount int        `json:"user_notes_count"`
+	Confidential   bool       `json:"confidential"`
+	DueDate        string     `json:"due_date"`
+	WebURL         string     `json:"web_url"`
 }
 
 func (i Issue) String() string {