Upgrade mongo.driver to 3.1.0

Author: yang-xiaodong

src/DotNetCore.CAP.MongoDB/DotNetCore.CAP.MongoDB.csproj

@@ -11,7 +11,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="MongoDB.Driver" Version="3.0.0" />
+    <PackageReference Include="MongoDB.Driver" Version="3.1.0" />
   </ItemGroup> 
 
 </Project>