Bump github.com/k8snetworkplumbingwg/network-attachment-definition-client from 0.0.0-20200331171230-d50e42f2b669 to 1.6.0

Bump github.com/k8snetworkplumbingwg/network-attachment-definition-client from 0.0.0-20200331171230-d50e42f2b669 to 1.6.0 #4