Bring Microsoft.NETCore.Platforms dependency back

Author: pakrym

samples/StaticFileSample/project.json

@@ -3,6 +3,7 @@
     "emitEntryPoint": true
   },
   "dependencies": {
+    "Microsoft.NETCore.Platforms": "1.0.1-*",
     "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0-*",
     "Microsoft.AspNetCore.Server.Kestrel": "1.0.0-*",
     "Microsoft.AspNetCore.StaticFiles": "1.0.0-*",

test/Microsoft.AspNetCore.StaticFiles.Tests/project.json

@@ -8,6 +8,7 @@
     "TestDocument.txt"
   ],
   "dependencies": {
+    "Microsoft.NETCore.Platforms": "1.0.1-*",
     "Microsoft.AspNetCore.StaticFiles": "1.0.0-*",
     "Microsoft.AspNetCore.TestHost": "1.0.0-*",
     "Microsoft.AspNetCore.Testing": "1.0.0-*",