#### 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
config,
          transitional.clarifyTimeoutError ? 'ETIMEDOUT' : 'ECONNABORTED',
          req
        ));
      });
    }
    if (config.cancelToken || config.signal) {
      
      
      onCanceled = function(cancel) {
        if (req.aborted) return;
        req.abort();
        reject(!cancel || (cancel && cancel.type) ? new Cancel('canceled') : cancel);
      };
      config.cancelToken && config.cancelToken.subscribe(onCanceled);
      if (config.signal) {
        config.signal.aborted ? onCanceled() : config.signal.addEventListener('abort', onCanceled);
      }
    }
    
    if (utils.isStream(data)) {
      data.on('error', function handleStreamError(err) {
        reject(enhanceError(err, config, null, req));
      }).pipe(req);
    } else {
      req.end(data);
    }
  });
};