added os tag, as its only available on win32

Author: Cory Fowler

src/Azure.Functions.Cli/npm/package.json

@@ -15,5 +15,6 @@
     "azfun": "lib/main.js",
     "azurefunctions": "lib/main.js"
   },
+  "os": ["win32"],
   "dependencies": {}
-}
+}