Consider tracking React version used by dash-renderer

[miqh]

Hello,

I recently had to help out building some custom React components for a Dash application and one big time sink I fell into was related to a React version discrepancy. It seems like other people probably run into this eventually too (#11).

The way in which I came to realise React 16 is yet to be supported was by checking the version of React being loaded the Dash application. This led me to the dash-renderer.

I suggest having the React version of this boilerplate track the one used by dash-renderer as an added measure to indicate which version is supported. For example, if any React 16 features are used, a user would see build failures when starting the app sandbox for developing a custom component.

[alexcjohnson]

Since this issue was opened we have first made React 16 a possibility, then finally a requirement for newer versions of Dash (starting a few versions prior to the current 1.0 release). But we haven't updated this repo to match - we need to do that!