Bump cross-spawn and webpack-cli

Bumps [cross-spawn](https://github.com/moxystudio/node-cross-spawn) to 6.0.6 and updates ancestor dependency [webpack-cli](https://github.com/webpack/webpack-cli). These dependencies need to be updated together.


Updates `cross-spawn` from 6.0.5 to 6.0.6
- [Changelog](https://github.com/moxystudio/node-cross-spawn/blob/v6.0.6/CHANGELOG.md)
- [Commits](moxystudio/node-cross-spawn@v6.0.5...v6.0.6)

Updates `webpack-cli` from 3.3.11 to 3.3.12
- [Release notes](https://github.com/webpack/webpack-cli/releases)
- [Changelog](https://github.com/webpack/webpack-cli/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-cli@v3.3.11...v3.3.12)

---
updated-dependencies:
- dependency-name: cross-spawn
  dependency-type: indirect
- dependency-name: webpack-cli
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>