Update Gravatar.swift (#298)
Update Gravatar.swift (#298)

Once sending the f parameters in the Query String the gravatar always force the the default image no matter the value of the parameter. 
As a simple test I've tried the following 4 URLs and only the last one returns my gravatar, the other 3 returns the default image: 
 - (https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=n&s=640)[https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=n&s=640]
 - (https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=y&s=640)[https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=y&s=640]
 - (https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=&s=640)[https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&f=&s=640]
 - (https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&s=640)[https://s.gravatar.com/avatar/3fe96e96013875d792fdf56fdc9da50d?d=mm&r=pg&s=640]
Alamofire/AlamofireImage,Alamofire/AlamofireImage