Why is the command 'add-migration' not accepting my installed packages in project.json?

After installing the microsoft.entityframework.tools -Pre/ and microsoft.entityframework.sqlserver, when using add-migration "InitialCreate", I have an error stating "build failed". Even when trying to explicitly build the project, it fails.

This is the error:

1>------ Build started: Project: OdeToFood, Configuration: Debug Any CPU ------
1>  C:\Program Files\dotnet\dotnet.exe build "C:\Users\Nazaqat\Documents\Visual Studio 2015\Projects\OdeToFood\src\OdeToFood" --configuration Debug --no-dependencies
1>C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\DotNet\Microsoft.DotNet.Common.Targets(262,5): error : Can not find runtime target for framework '.NETCoreApp,Version=v1.0' compatible with one of the target runtimes: 'win10-x64, win81-x64, win8-x64, win7-x64'. Possible causes:
1>C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\DotNet\Microsoft.DotNet.Common.Targets(262,5): error : 1. The project has not been restored or restore failed - run `dotnet restore`
1>C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\DotNet\Microsoft.DotNet.Common.Targets(262,5): error : 2. The project does not list one of 'win10-x64, win81-x64, win8-x64, win7-x64' in the 'runtimes' section.
1>C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\DotNet\Microsoft.DotNet.Common.Targets(262,5): error : 3. You may be trying to publish a library, which is not supported. Use `dotnet pack` to distribute libraries.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

My Project.json file looks like this:

{

  "dependencies": {
    "Microsoft.AspNetCore.Diagnostics": "1.1.0",
    "Microsoft.AspNetCore.Mvc": "1.1.0",
    "Microsoft.AspNetCore.Server.IISIntegration": "1.1.0",
    "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final",
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.StaticFiles": "1.1.0",
    "Microsoft.EntityFrameworkCore": "1.1.0",
    "Microsoft.EntityFrameworkCore.Design": "1.1.0",
    "Microsoft.EntityFrameworkCore.SqlServer": "1.1.0",
    "Microsoft.EntityFrameworkCore.Tools": "1.1.0-preview4-final",
    "Microsoft.Extensions.Configuration.FileExtensions": "1.1.0",
    "Microsoft.Extensions.Configuration.Json": "1.1.0",
    "Microsoft.Extensions.Logging.Console": "1.1.0",
    "Microsoft.NETCore.App": "1.1.0"
  },

  "tools": {
    "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final",
    "Microsoft.EntityFrameworkCore.Tools": "1.1.0-preview4-final"
  },

  "frameworks": {
    "netcoreapp1.0": {
      "imports": [
        "dotnet5.6",
        "portable-net45+win8"
      ]
    }
  },

  "buildOptions": {
    "emitEntryPoint": true,
    "preserveCompilationContext": true
  },

  "runtimeOptions": {
    "configProperties": {
      "System.GC.Server": true
    }
  },

  "publishOptions": {
    "include": [
      "wwwroot",
      "web.config"
    ]
  },

  "scripts": {
    "postpublish": [ "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%" ]
  }
}

After looking online, I saw a solution which was to add the following runtime section into the project.json file - which makes the solution build successfully:

"runtimes": {
    "win10-x64": { }
  }

However when using 'add migration "InitialCreate"' inside the Package Manager Console, I get the error:

Cannot execute this command because Microsoft.EntityFrameworkCore.Design is not installed. Install the version of that package that matches the installed version of Microsoft.EntityFrameworkCore and try again. 

Even though I have all the installed packages in the above project.json file.