Add dotnetcore NuGet repo back

nuget.config

@@ -2,6 +2,7 @@
 <configuration>
   <packageSources>
     <add key="aspnetrelease" value="https://www.myget.org/F/aspnetrelease/" />
+    <add key="dotnetcore" value="https://www.myget.org/F/dotnet-core/" />
     <add key="nuget.org" value="https://www.nuget.org/api/v2/" />
   </packageSources>
   <disabledPackageSources />

src/Microsoft.PowerShell.Linux.Host/project.json

@@ -12,7 +12,7 @@
 
     "dependencies": {
 	"Microsoft.NETCore.Runtime": "1.0.1-beta-*",
-        "Microsoft.Extensions.PlatformAbstractions": "1.0.0-*",
+        "Microsoft.Extensions.PlatformAbstractions": "1.0.0-rc1-16231",
         "System.Management.Automation": "",
         "Microsoft.PowerShell.Security": "",
         "Microsoft.PowerShell.Commands.Utility": "",