Deprecated lifecycle hooks

[olehreznichenko]

Feature Request

https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html
It will be good to migrate to new hooks.

https://github.com/jscottsmith/react-scroll-parallax/blob/master/src/components/ParallaxProvider.js#L20
https://github.com/jscottsmith/react-scroll-parallax/blob/master/src/components/Parallax.js#L69

[jscottsmith]

will fix in v2: see #47