Summary: Without specifying the deployment target, it was default to iOS 4.3. This would cause a build error because we are `unable to synthesize weak properties` which didn't come around until iOS 5. Setting default target to iOS 8.
Reviewed By: emilsjolander
Differential Revision: D4481772
fbshipit-source-id: d3be88d0f73533c6242fc1d9045c70ad4628fd21