PR for usage in non-browser environments

[Metavirulent]

I created PR #25 so react-tippy can be used in non-browser environment. This is critical because otherwise the component breaks all tests that don't run on selenium, e.g. jest or enzyme tests that mount the component to unit test it.

[combizs]

Try checking out using it with enzyme, you can gather a shallow/deep JSON snapshot.

https://github.com/adriantoine/enzyme-to-json#helper