Update copyright headers (#433)

Summary:
Style is modified, so I think it's okay to add
our header there too.
Pull Request resolved: https://github.com/facebook/flipper/pull/433

Differential Revision: D15213091

Pulled By: passy

fbshipit-source-id: c02b67b022f12fdb3e0da39a308d33b073dcb9d3

static/style.css

@@ -1,6 +1,7 @@
 /* http://meyerweb.com/eric/tools/css/reset/
    v2.0 | 20110126
    License: none (public domain)
+   Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
 */
 
 html,