#### 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.strictEqual(error.message, 'oops, timeout');
        done();
      }, 300);
    });
  });
  it('should allow passing JSON', function (done) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json');
      res.end(JSON.stringify(data));
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').then(function (res) {
        assert.deepEqual(res.data, data);
        done();
      });
    });
  });
  it('should allow passing JSON with BOM', function (done) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json');
      var bomBuffer = Buffer.from([0xEF, 0xBB, 0xBF])