Issue Summary

with the change from request to axios, the outgoing requests have now 2 user agent headers:

• 'User-agent': 'sendgrid/7.0.0;nodejs'
• 'User-Agent': 'axios/0.19.2'

this makes our testing with nock fail, because it tries to lower-case all headers and breaks when there is a conflict.

Steps to Reproduce

1. create a mock server to receive requests made with the sdk
2. inspect any incoming request header

Code Snippet

sendgrid adds the user agent header with uppercase "U" and lowercase "a"

but axios just checks for the header with "u" + "a" or "U" + "A"
https://github.com/axios/axios/blob/42eb9dfabc85ed029462da1c503f8b414b08ffd0/lib/adapters/http.js#L34

if (!headers['User-Agent'] && !headers['user-agent']) {

Exception/Log

the resulting request has both headers:

headers: {
  Accept: 'application/json',
  'Content-Type': 'application/json',
  'User-agent': 'sendgrid/7.0.0;nodejs',
  Authorization: 'Bearer SG.fakeKey',
  'User-Agent': 'axios/0.19.2',
  'Content-Length': 360
}

Technical details:

• sendgrid-nodejs version: 7.0.0
• node version: 12.13.1