Bumped demo's target version to `8.0`. Fixed deprecated warnings.

NOTE: `AutoLayoutTextViews` WILL continue to support iOS 7.0+. The only reason the demo is `8.0+` is for ease in showcasing an `ALAutoResizingTextView` within a table view cell.
If you need to support iOS 7.0+, check out `AutoLayoutCells` repo, which has a dependency on `AutoLayoutTextViews`.