#### Is your feature request related to a problem? Please describe.
This is an optimazition of code.

#### Describe the solution you'd like
The following line of code comes from https://github.com/axios/axios/blob/master/lib/adapters/http.js#L403:
```js
reject(!cancel || (cancel && cancel.type) ? new CanceledError() : cancel);
```
It can be optimized as follows:
```js
reject(!cancel || cancel.type ? new CanceledError() : cancel);
```

#### Describe alternatives you've considered
When the code is executed to `(cancel && cancel.type)`, it means `!cancel` is false, so `cancel` is true, we can get `cancel.type` directly.

#### Additional context
no more

lib/adapters/http.js
config
        ));
      }
      
      if (!headerNames['content-length']) {
        headers['Content-Length'] = data.length;
      }
    }
    
    var auth = undefined;
    if (config.auth) {
      var username = config.auth.username || '';
      var password = config.auth.password || '';
      auth = username + ':' + password;
    }
    
    var fullPath = buildFullPath(config.baseURL, config.url);
    var parsed = url.parse(fullPath);
    var protocol = parsed.protocol || supportedProtocols[0];
    if (supportedProtocols.indexOf(protocol) === -1) {
      return reject(new AxiosError(
        'Unsupported protocol ' + protocol,
        AxiosError.ERR_BAD_REQUEST,
        config
      ));
    }
    if (!auth && parsed.auth) {
      var urlAuth = parsed.auth.split(':');
      var urlUsername = urlAuth[0] || '';
      var urlPassword = urlAuth[1] || '';