#### Describe the bug
The irrelevant error returned when requesting illegal URL, like: "tel:484-695-3408"
```
TypeError: Cannot read property 'replace' of null
    at dispatchHttpRequest (node_modules/axios/lib/adapters/http.js:109:74)
    at new Promise (<anonymous>)
    at httpAdapter (node_modules/axios/lib/adapters/http.js:46:10)
    at dispatchRequest (node_modules/axios/lib/core/dispatchRequest.js:52:10)
```

#### To Reproduce
```js
axios.get('tel:484-695-3408').catch(err => console.error(err));
```

#### Expected behavior
Return descriptive error, like "Unsupported protocol tel:"

#### Environment
 - Axios Version: 0.21.1
 - Adapter: HTTP
 - Browser: none
 - Browser Version: none
 - Node.js Version: 12.19.0
 - OS: MacOS 10.14
 - Additional Library Versions: none

#### Additional context/Screenshots
none
test/unit/adapters/http.js
assert.equal(resp.status, 200);
          assert.equal(resp.statusText, 'OK');
          done();
        })
        .catch(function (error) {
          assert.ifError(error);
          done();
        });
    });
  });
  it('should support streams', function (done) {
    server = http.createServer(function (req, res) {
      req.pipe(res);
    }).listen(4444, function () {
      axios.post('http://localhost:4444/',
        fs.createReadStream(__filename), {
          responseType: 'stream'
        }).then(function (res) {
          var stream = res.data;
          var string = '';
          stream.on('data', function (chunk) {
            string += chunk.toString('utf8');
          });
          stream.on('end', function () {
            assert.equal(string, fs.readFileSync(__filename, 'utf8'));
            done();
          });
        });
    });
  });