chore(mocha): provide global.document stub for React shallowRenderer
chore(mocha): provide global.document stub for React shallowRenderer

Issue:
======

When using `shallowRenderer` tests invokes `setState` the test will fail
with a `document is not defined` reference error.

Job Story:
==========

When I write test that invokes `setState`, I want it to pass, so that I
don't have to install jsdom.

Approach:
=========

Provide a `global.document` mock as part of the mocha config

import expect from 'expect';
import { add } from '../src';

import React from 'react/addons';

Test case:
==========
    describe('shallowRenderer event tests work without jsdom', () => {
      class Tester extends React.Component {
        constructor(props) {
          super(props);
          this.state = { foo: "bar" };
          this.handleClick = () => { this.setState({foo: "baz"}) };
        }
        render () {
          return <div onClick={this.handleClick}>{this.state.foo}</div>;
        }
      }

      let shallowRenderer = React.addons.TestUtils.createRenderer();

      it('shallow renderer works', () => {
        shallowRenderer.render(<Tester />);
        let result = shallowRenderer.getRenderOutput();
        expect(result.props.children).toBe("bar");

        result.props.onClick();
        let newResult = shallowRenderer.getRenderOutput();
        expect(newResult.props.children).toBe("baz");
      });
    });

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