Fix a typo of storlet engine overview document
Fix a typo of storlet engine overview document

Current document says "All the storlets being executed on data
objects belonging to SOME account, will be executed in the same
Docker container." But SOME is not correct, SAME is correct.
This patch fixes the small typo.

Change-Id: I4974506eaa5b438f7ca1f97fedca683c8574e033

openstack/storlets,openstack/storlets,openstack/storlets,openstack/storlets