Update spectacle-code-slide to work with Spectacle 4.0 and React 16

[nwaywood]

Atm spectacle-code-slide is broken using Spectacle 4 and React 16

Steps to reproduce:

1. Clone the spectacle boilerplate
2. yarn add spectacle-code-slide
3. Try and use CodeSlide component
4. Get the error shown above

[kitten]

Since this is not our library we can’t do much to fix it ASAP, but there’s a PR open over at the spectacle-code-slide repo: jamiebuilds/spectacle-code-slide#45

[nwaywood]

Ok thanks, I'll keep an eye on that PR. cc @thejameskyle

[kenwheeler]

Done