http(s)Agent not sent properly to follow-redirects

[mhassan1]

Describe the bug
In #2426, axios started passing agents to follow-redirects; however, the documentation for follow-redirects shows the shape of agents differently than what axios is passing. It means that an alternative agent is not correctly resolved by follow-redirects.

To Reproduce
Pass in an httpsAgent with an invalid configuration, which should cause axios.request to reject. In 0.19.0, it rejects; on master, it does not. See code snippet below.

require('axios')({
  url: 'https://postman-echo.com/get',
  httpsAgent: new require('https').Agent({
    ciphers: 'does-not-exist'
  })
}).catch(err => console.error(err.message))

Expected behavior
httpsAgent should be passed to follow-redirects

Environment:

• Axios Version: master (unreleased 0.19.1)
• OS: OSX 10.15
• Node 8

[chinesedfan]

Solved by #1904 and released to 0.19.1 yet.