**Describe the bug**
Unit test case failed :
  1) supports http with nodejs
       should pass errors for a failed stream:
     Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (***************...

**To Reproduce**
Use VS Code internal terminal to excute the unit test .

**Expected behavior**
UT should be excuted correctly.

**Environment:**
 - Axios Version: latest master
 - OS Version: Window 10

**Additional context/Screenshots**
![Capture](https://user-images.githubusercontent.com/46782518/70436361-136c5380-1ac4-11ea-87b5-203b2e46ebbf.PNG)

test/unit/adapters/http.js
axios.get('http://localhost:4444/', {
          proxy: {
            host: 'localhost',
            port: 4000
          }
        }).then(function (res) {
          assert.equal(res.data, '123456789', 'should pass through proxy');
          done();
        });
      });
    });
  });
  it('should not pass through disabled proxy', function (done) {
    // 
    process.env.http_proxy = 'http://does-not-exists.example.com:4242/';
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'text/html; charset=UTF-8');
      res.end('123456789');
    }).listen(4444, function () {
      axios.get('http://localhost:4444/', {
        proxy: false
      }).then(function (res) {
        assert.equal(res.data, '123456789', 'should not pass through proxy');
        done();
      });
    });
  });
  it('should support proxy set via env var', function (done) {
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'text/html; charset=UTF-8');