Propose to move react and react-dom to peerDependencies

[Kudo]

Currently react and react-dom specified as dependencies in package.json.
If user use next React version, e.g. React v16, there will have some unexpected dependencies in node_modules.
Here to propose move them as peerDependencies.

[IanVS]

The dependencies will only be there for development builds though. If installing only production modules, as long as flow-coverage-report is listed as a devDepencency, it won't get installed.

[swac]

Any update here? It feels weird to have React 15 in our dependency graph, even if it's just a dev dependency.

[NameFILIP]

I noticed React 15 in the dependency graph as well today. Any ideas on how this can be solved?