Bump webpack from 1.15.0 to 2.7.0

Bumps [webpack](https://github.com/webpack/webpack) from 1.15.0 to 2.7.0.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v1.15.0...v2.7.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]