Convert some CommonJS constructs to ES6

Summary:
Tried to automate this with [cjs-to-es6](https://github.com/nolanlawson/cjs-to-es6) but it only
works on vanilla JS files without any special Flow syntax. I converted some places
manually but we can just do the rest as we modify the files.

Reviewed By: jknoxville

Differential Revision: D16340187

fbshipit-source-id: b55c7ce2d719876e47e85f5f3fce13b8c8ae4010

src/utils/info.js

@@ -5,7 +5,7 @@
  * @format
  */
 
-const os = require('os');
+import os from 'os';
 
 export type Info = {
   arch: string,