Update health-checking.md (#2785)
Update health-checking.md (#2785)

Fixed spell error: spec.health.failureTheshold to spec.health.failureThreshold
googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones,googleforgames/agones