Describe the bug

The new React context elements (https://reactjs.org/docs/context.html) report their type as objects instead of functions (custom react components) or strings (native react components), which breaks dive(). I haven't tested whether other methods of ShallowWrapper break.

To Reproduce

https://codesandbox.io/s/zxj4898zxp?module=%2Fsrc%2FApp.test.js

Expected behavior

shallow and dive should implement actual render semantics when handling the new context API:

1. Automatically update current context whenever a context provider is encountered and remove the provider node from the tree.
2. Automatically pass the current context to childs of context consumer nodes and remove the consumer node from the tree.

I'm sure the above are not the exact semantics, but at least the most intuitive.