Compiler config format from docs does not work

[cpmsmith]

While the docs say to make a relay.config.js file which exports an object, doing so doesn't actually work, as the compiler expects the file to be JSON, even if it is named relay.config.js.

Basic reproduction here: https://glitch.com/edit/#!/statuesque-jeweled-condorraptor

Here's what happens when you try to use different config files:

relay.config.actually-json.js is in JSON format, despite being named .js.