Bump commander from 5.1.0 to 6.1.0

Bumps [commander](https://github.com/tj/commander.js) from 5.1.0 to 6.1.0.
- [Release notes](https://github.com/tj/commander.js/releases)
- [Changelog](https://github.com/tj/commander.js/blob/master/CHANGELOG.md)
- [Commits](tj/commander.js@v5.1.0...v6.1.0)

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

Author: dependabot[bot]

package-lock.json

@@ -9,7 +9,7 @@
     "url": "https://github.com/jupyterhub/configurable-http-proxy.git"
   },
   "dependencies": {
-    "commander": "~5.1.0",
+    "commander": "~6.1.0",
     "http-proxy": "^1.18.1",
     "lynx": "^0.2.0",
     "strftime": "~0.10.0",