Add netstandard 2.0 target on WindowsServer and DependencyCollector

[lmolkova]

All .net core libs should target 2.0

[lmolkova]

netstandard 2.0 target does not require additional dependencies on

WindowsServer
NETStandard.Library (>= 1.6.1)
System.Runtime.Serialization.Json (>= 4.3.0)
System.Runtime.Serialization.Primitives (>= 4.3.0)

DependecnyCollector:
NETStandard.Library (>= 1.6.1)
System.Data.SqlClient (>= 4.3.1)
System.Diagnostics.StackTrace (>= 4.3.0)

[cijothomas]

Thanks for opening this. We can try to do this in next release.