Circular crashing with iOS 10

[stemberamichal]

Key-value observation using closure crashes with:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason:
'An instance of class UIView was deallocated while key value observers were still registered with it.

Works fine with iOS 11, because the observation is removed when ObservationInfo is reeased.

Possible solutions are:

• Use different mechanic to observe \UView.bounds
• Limit support for iOS 11.0+

[stemberamichal]

Do not have to forget to update readme and podspec to contain possible changes to supported version.