Update the version of Microsoft.AspNetCore.Server.Testing to RTM version number

Author: pranavkm

test/Microsoft.AspNetCore.Server.IISIntegration.FunctionalTests/project.json

@@ -18,7 +18,7 @@
   },
   "dependencies": {
     "dotnet-test-xunit": "1.0.0-rc3-000000-01",
-    "Microsoft.AspNetCore.Server.Testing": "1.0.0-rc2-20896",
+    "Microsoft.AspNetCore.Server.Testing": "0.1.0-rtm-21431",
     "Microsoft.Extensions.Logging": "1.0.0",
     "Microsoft.Extensions.Logging.Console": "1.0.0",
     "Microsoft.Extensions.Logging.Debug": "1.0.0",