Could not load file or assembly 'Microsoft.EntityFrameworkCore.SqlServer, Version=1.1.0.0' after upgrading to 1.1.0

Complete project references clean-up solved my problem.

1. Delete all bin/obj folders
2. Delete all project.lock.json files
3. Delete local Nuget repository cache (computer one)
4. Remove all references from project.json file and add only required ones (with the help of R#)
5. nuget udpate, dotnet restore = project is running

When I'm thinking about it again, maybe only point 4 was important?