Update packages' versions

Author: troydai

src/Microsoft.AspNet.Tooling.Razor/project.json

@@ -13,7 +13,7 @@
         },
         "dnxcore50" : {
             "dependencies": {
-                "System.Runtime": "4.0.20-*"
+                "System.Runtime": "4.0.21-beta-*"
             }
         }
     }