Updating json files to pin versions and build.cmd to pin KoreBuild and DNX

Author: pranavkm

src/Microsoft.Framework.OptionsModel/project.json

@@ -6,7 +6,7 @@
         "Microsoft.Framework.DependencyInjection.Abstractions": "1.0.0-beta8",
         "Microsoft.Framework.NotNullAttribute.Sources": {
             "type": "build",
-            "version": "1.0.0-*"
+            "version": "1.0.0-beta8"
         }
     },
     "repository": {