hubot-slack security issue - Machine-In-The-Middle - https-proxy-agent

[xtagon]

npm audit reported a lot of security issues. All of them went away after updating a few NPM packages, except one:

                       === npm audit security report ===                        
                                                                                
# Run  npm update https-proxy-agent --depth 3  to resolve 1 vulnerability
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High          │ Machine-In-The-Middle                                        │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ https-proxy-agent                                            │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ hubot-slack                                                  │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ hubot-slack > @slack/client > https-proxy-agent              │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://npmjs.com/advisories/1184                            │
└───────────────┴──────────────────────────────────────────────────────────────┘


found 1 high severity vulnerability in 908 scanned packages
  run `npm audit fix` to fix 1 of them.

Blocked by slackapi/hubot-slack#578