chore(dependencies): upgrade react, react-router, and jest

[mcbryant]

The goal of this patch is to resolve warnings present when using Belle in a React 15.x codebase. This patch should not change the behaviour of Belle.

Details:

• tests, docs, and examples: upgraded to React 15.x
• docs: upgraded to React Router 2.5.2 for compatibility with React 15.x (see https://github.com/ReactTraining/react-router/issues/3695)
• src, tests, docs, and examples: fixed various warnings introduced throughout React 15.x
• tests: upgraded Jest for compatibility with Node 6 (https://github.com/facebook/jest/issues/1088)

Testing:

• verified that there were no React-related warnings in tests, docs, and examples
• browsed docs and examples in Chrome and FF

[mcbryant]

Note: This can be applied to the v3 branch with small changes. I'll make a PR once this is merged.

[nikgraf]

@mcbryant I believe from all I learned v3 will be started over in a few months.

After this awesome contribution I will give you commit writes. Interested to contribute more?

[mcbryant]

I'm definitely interested! Thank you for your consideration, and I'll see what I can do!

[nikgraf]

@mcbryant feel free to ping me anytime on Twitter or here. I have some ideas, but too little time 😄