#### 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
var url = require('url');
var zlib = require('zlib');
var assert = require('assert');
var fs = require('fs');
var path = require('path');
var pkg = require('./../../../package.json');
var server, proxy;
describe('supports http with nodejs', function () {
  afterEach(function () {
    if (server) {
      server.close();
      server = null;
    }
    if (proxy) {
      proxy.close();
      proxy = null;
    }
    if (process.env.http_proxy) {
      delete process.env.http_proxy;
    }
    if (process.env.no_proxy) {
      delete process.env.no_proxy;
    }
  });
  it('should throw an error if the timeout property is not parsable as a number', function (done) {
    server = http.createServer(function (req, res) {
      setTimeout(function () {
        res.end();
      }, 1000);
    }).listen(4444, function () {