Update superagent and superagent-proxy dependencies

[katafractari]

Addressing #128
Tests are green in my local environment. We are already using this version in our application without any apparent problems.

[kenjinsama]

I approve this since it cause many problems with proxies that were resolved since : TooTallNate/node-agent-base#35

See the dependencies:

npm ls agent-base
fc@0.0.2 /home/stephane/Projets/franceconnect/fc/back
└─┬ node-mailjet@3.3.1
  └─┬ superagent-proxy@1.0.3
    └─┬ proxy-agent@2.3.1
      ├── agent-base@4.3.0 
      ├─┬ http-proxy-agent@2.1.0
      │ └── agent-base@4.3.0  deduped
      ├─┬ https-proxy-agent@2.2.4
      │ └── agent-base@4.3.0  deduped
      ├─┬ pac-proxy-agent@2.0.2
      │ └── agent-base@4.3.0  deduped
      └─┬ socks-proxy-agent@3.0.1
        └── agent-base@4.3.0  deduped

[satyavh]

This merge is required for Mailjet not conflicting with other packages. When will this be merged?

[kenjinsama]

Is there still someone here that maintains the pull requests 😢 ?