Bump npm from 5.7.1 to 6.13.4

Bumps [npm](https://github.com/npm/cli) from 5.7.1 to 6.13.4.
- [Release notes](https://github.com/npm/cli/releases)
- [Changelog](https://github.com/npm/cli/blob/latest/CHANGELOG.md)
- [Commits](https://github.com/npm/cli/compare/v5.7.1...v6.13.4)

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

package.json

@@ -12,7 +12,7 @@
   "license": "ISC",
   "dependencies": {
     "hash.js": "^1.1.3",
-    "npm": "^5.7.1",
+    "npm": "^6.13.4",
     "xml-formatter": "^1.0.1",
     "xmldom": "^0.1.27",
     "xpath": "0.0.24"