[v2] PageRenderer exported from gatsby doesn't work in production

[pieh]

https://github.com/gatsbyjs/gatsby/blob/v2/packages/gatsby/src/cache-dir/gatsby-browser-entry.js#L8-L15
JSONStore used there isn't used in production anywhere else and will never render anything in production. My hacky solution to use page-renderer.js directly instead of JSONStore there for production builds seems to work, but I need to investigate it more and figure out not hacky solution to make it work for both production and development.

For reference - here's hacky fix - pieh@fc3b255

[KyleAMathews]

Seems like a reasonable hack :-) Main thing is to avoid loading any extra code into production.