Docker version 1.9 was released recently which introduced substantial new
features including a nearly complete re-working of networking (while still
supporting backwards compatibility).

This is a very important new version introducing concepts and objects which are
similar to networking found in other virtual technologies (while not being the
same or likely compatible with others like KVM, VBox, Xen, VMware, etc).

As a significant new version, updating is probably to this version is likely
more important than an ordinary new version.