#### 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
lib/adapters/http.js
stream.on('error', function handleStreamError(err) {
          if (req.aborted) return;
          reject(enhanceError(err, config, null, lastRequest));
        });
        stream.on('end', function handleStreamEnd() {
          try {
            var responseData = responseBuffer.length === 1 ? responseBuffer[0] : Buffer.concat(responseBuffer);
            if (config.responseType !== 'arraybuffer') {
              responseData = responseData.toString(config.responseEncoding);
              if (!config.responseEncoding || config.responseEncoding === 'utf8') {
                responseData = utils.stripBOM(responseData);
              }
            }
            response.data = responseData;
          } catch (err) {
            reject(enhanceError(err, config, err.code, response.request, response));
          }
          settle(resolve, reject, response);
        });
      }
    });
    
    req.on('error', function handleRequestError(err) {
      if (req.aborted && err.code !== 'ERR_FR_TOO_MANY_REDIRECTS') reject(err);
      reject(enhanceError(err, config, null, req));
    });
    
    req.on('socket', function handleRequestSocket(socket) {
      
      socket.setKeepAlive(true, 1000 * 60);