Fixed MessageProperties serialzation bug.
Fixed MessageProperties serialzation bug.

Pliner/EasyNetQ.Management.Client,Pliner/EasyNetQ.Management.Client,EasyNetQ/EasyNetQ.Management.Client,alexwiese/EasyNetQ.Management.Client,micdenny/EasyNetQ.Management.Client,EasyNetQ/EasyNetQ.Management.Client,chinaboard/EasyNetQ.Management.Client,LawrenceWard/EasyNetQ.Management.Client,micdenny/EasyNetQ.Management.Client