Last line of agnostic-usage.

[jdalton]

The last line of agnostic-usage:

Because this proposal retains the .js suffix, applications that require a module that ends in .js, a standard practice, will continue to work even if the package in question updates to use standard modules and does not publish a poly-package.

Should clarify that "in versions of Node which support standard modules" a poly-package may not be required (though maybe a better example should be used).