WIP: Loosen the pinning on "ohai"

Ohai requirement of ~> 8.0 is incompatible with Chef 13 or newer.

Unpin the requirement a little to allow for Ohai up to 14.x, as for omnibus's needs the Ohai API should be stable up through Chef/Omnibus 14

Signed-off-by: Richard Clamp richardc@unixbeard.net