allowing isProduction to be passed in as an option to the build process

Here's my use case for this - I'd like to build a "staging" version of the app that is functionally identical to production, but points to a different url. I don't want to skip running minification/fingerprinting/WhatHaveYou but I don't want to run the risk of missing a setting. I'd rather just set an option at build time to ensure the production/staging builds are identical.