doc: fix typo

Signed-off-by: yorkie <yorkiefixer@gmail.com>
(cherry picked from commit d2c5bf23f16a98ca6f603f7fe2b5a31c70d4c8db)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/userguide/networking/dockernetworks.md

@@ -18,7 +18,7 @@ applications run on. Docker container networks give you that control.
 
 This section provides an overview of the default networking behavior that Docker
 Engine delivers natively. It describes the type of networks created by default
-and how to create your own, user--defined networks. It also describes the
+and how to create your own, user-defined networks. It also describes the
 resources required to create networks on a single host or across a cluster of
 hosts.