Don't allow rejecting with non-error objects

Summary: This will make it easier to handle errors, because you know you can get the message out, along with stack trace, without having to deal with potentially any object that could be passed in.

Reviewed By: passy

Differential Revision: D16006180

fbshipit-source-id: f200965d7663c5f8a471603fceb6b4cdbea73381

.eslintrc.js

@@ -24,6 +24,7 @@ module.exports = {
     'max-len': 0, // let's take prettier take care of this
     indent: 0, // let's take prettier take care of this
     'no-console': 0, // we're setting window.console in App.js
+    'prefer-promise-reject-errors': 1,
 
     // additional rules for this project
     'header/header': [2, 'block', {pattern}],