* add global.document to test enviorment for setState tests

This curcumvents a bug ir React. You can see a manifestation of it [here](facebook/react#4019).

This existence of a `document` is required by React, when using `setState`. While `shallowRenderer` is inteded for use without a document, all tests that use `setState` will fail with a `documentis not defined`reference error.

Fortunately, React doesn't need anything more than the existance of the global. So, we can define it in our test environment.

This is where a more robust environment could be setup, using [jsdom](https://www.npmjs.com/package/jsdom) if needed.

test/mocha.opts

@@ -1 +1,2 @@
+--require test/utils/document.js
 --compilers js:babel/register

test/utils/document.js

@@ -0,0 +1 @@
+global.document = {};