Updated Json.Net version

Author: ajaybhargavb

tools/Microsoft.AspNetCore.Server.Kestrel.LibuvCopier/project.json

@@ -5,7 +5,7 @@
   },
   "dependencies": {
     "Microsoft.Extensions.PlatformAbstractions": "1.0.0-*",
-    "Newtonsoft.Json": "8.0.2"
+    "Newtonsoft.Json": "8.0.3"
   },
   "frameworks": {
     "netstandardapp1.5": {