`npx electron-webpack dev -- --version` improper behavior

* **Version**: 2.7.4
* **Target**: MacOS

When running `npx electron-webpack dev -- --version`, my program receives `-- --version` as input `argv`, which is wrong. The `--` should be consumed by `electron-webpack` as this is a standard way to tell that all args after `--` should be passed to the sub-command.

Start by reproducing `npx electron-webpack dev -- --version` on the reported setup, then trace the `electron-webpack dev` command's argument parsing. Done means the separator is consumed and the Electron program receives only `--version`, with the existing command behavior preserved.

Written by the indexing model from the issue text.