Bump webpack-node-externals from 1.7.2 to 3.0.0

Bumps [webpack-node-externals](https://github.com/liady/webpack-node-externals) from 1.7.2 to 3.0.0.
- [Release notes](https://github.com/liady/webpack-node-externals/releases)
- [Changelog](https://github.com/liady/webpack-node-externals/blob/master/CHANGELOG.md)
- [Commits](liady/webpack-node-externals@v1.7.2...v3.0.0)

---
updated-dependencies:
- dependency-name: webpack-node-externals
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

package.json

@@ -18,7 +18,7 @@
     "babel-preset-stage-3": "^6.24.1",
     "serverless-webpack": "^3.1.0",
     "webpack": "^3.6.0",
-    "webpack-node-externals": "^1.6.0"
+    "webpack-node-externals": "^3.0.0"
   },
   "dependencies": {
     "babel-runtime": "^6.26.0",