Entity with invulnerable tag is not invulnerable

What I expected to happen was...:
The shulker that I was spawning was supposed to be invulnerable

What actually happened was...:
It wasn't invulnerable

Steps to Reproduce:
1. Write the command:  /summon shulker ~ ~ ~ {Invulnerable:1}
2. The shulker will not be invulnerable