Can the Weapon Master feat be used to gain proficiency with natural weapons?

@JeremyECrawford Can the Weapon Master feat be used to gain proficiency with natural weapons? Or even just "Claw" or "Bite" proficiency?

— Joshua Castle (@Jmnc4Dnd) April 28, 2016

As clarified in the PH errata, Weapon Master gives you proficiency with simple/martial weapons only. #DnD https://t.co/93HAwM3tyH

— Jeremy Crawford (@JeremyECrawford) May 3, 2016