Bump npm from 6.13.1 to 6.13.4

Bumps [npm](https://github.com/npm/cli) from 6.13.1 to 6.13.4.
- [Release notes](https://github.com/npm/cli/releases)
- [Changelog](https://github.com/npm/cli/blob/latest/CHANGELOG.md)
- [Commits](npm/cli@v6.13.1...v6.13.4)

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

package.json

@@ -1716,7 +1716,7 @@
         "lodash": "^4.17.14",
         "lodash.isequal": "4.5.0",
         "net": "1.0.2",
-        "npm": "^6.13.1",
+        "npm": "^6.13.4",
         "open": "^6.3.0",
         "paredit.js": "^0.3.6",
         "parinfer": "^3.12.0",