Apply security update suggestions
Apply security update suggestions

Summary:
Manually applying these "fixes":

- fixes https://github.com/facebook/flipper/pull/480
- fixes https://github.com/facebook/flipper/pull/481

This is mainly to sush the security warnings we get
even though we don't really have an attack surface where these matter.

Reviewed By: danielbuechele

Differential Revision: D16148208

fbshipit-source-id: 79865a97b442fd2b2621f1ef632e974e1e355e84

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper