Update package.json

version 5.0.0 has security warning

Author: ArcEye

machinetalk-protobuf/package.json

@@ -24,7 +24,7 @@
   "homepage": "https://github.com/machinekit/machinetalk-protobuf#readme",
   "dependencies": {
     "mkdirp": "0.5.1",
-    "protobufjs": "5.0.0"
+    "protobufjs": "5.0.3"
   },
   "devDependencies": {
     "browserify": "^13.0.0",