Remove propTypes in production

This will help reduce the bundle size impact. Note that any consumers
who are depending on any react-dates components having a `.propTypes`
property will no longer work as expected after this change.

I enabled this using wrap mode, which adds `process.env.NODE_ENV`
checks, which is a pretty standard method for React apps. I believe this
will allow this library to have propTypes in development, but for them
to be minified out in production builds.

To make this safe to enable in this repo, I enabled the
react/forbid-foreign-prop-types ESLint rule, which was written
specifically for the benefit of this plugin.

Here's a diff showing what effect this has on the esm build:

  https://gist.github.com/lencioni/1b436d365570394ccde659c829ba02c3