remove experimental "modules" support
remove experimental "modules" support

This was causing a bug: https://github.com/feross/standard/issues/148

It's really an eslint bug: https://github.com/eslint/eslint/issues/2636

I'm going to just remove support for ES6 modules until this is fixed,
since it's marked "experimental" in eslint. If people really want ES6
modules, they can use a custom parser like babel-eslint (now supported).

bengl/eslint-config-standard,valedaemon/eslint-config-postmodern,feross/eslint-config-standard,keis/eslint-config-standard,xjamundx/eslint-config-standard