If a Shadow rolls a critical does it do 2d4 strength damage?

@mikemearls @JeremyECrawford If a Shadow rolls a critical, does it do 2d4 strength damage, as well as the necroctic damage?

— King Wizard (@_Matafer) February 12, 2016

A critical hit lets you roll damage dice twice. The shadow's Strength reduction isn't damage. #DnD https://t.co/m0MCEJGvPq

— Jeremy Crawford (@JeremyECrawford) February 12, 2016