#### Is your feature request related to a problem? Please describe.
Axios 0.21.1 does not cope with requests through proxy to secured URLs - HTTP code 501 is received.
I'm behind corporate network. When I try to launch the following code, the error 501 is received:
```
const axios = require("axios");

axios.get('https://jsonplaceholder.typicode.com/todos/12', {
    proxy: {
        protocol: 'http',
        host: 'corporate.proxy',
        port: 9000
    },
})
    .then(response => response.data)
    .then(data => console.log(data))
    .catch((error) => {
        const errorMessage = error.message;
        const responseData = error.response && error.response.data;
        console.log('error')
        console.log(`${errorMessage}${
            responseData
            && typeof responseData === 'object'
                ? `: ${JSON.stringify(responseData)}`
                : ''}`)
    });
```

Requests made to unsecured URLs - http protocol - with or without proxy settings succeed.

#### Describe the solution you'd like
Fix or implement please a possibility to perform requests to secured URLs - https protocol - through proxy.

#### Describe alternatives you've considered
Instead of using "axios" module, the module "axios-https-proxy-fix" solves the issue. However, it's some old fix. And most probably does not update to new features that original Axios may bring. Definitely I would like to stick to primary.

#### Additional context
No solution is found around the original source.

lib/adapters/http.js
statusText: res.statusMessage,
        headers: res.headers,
        config: config,
        request: lastRequest
      };
      if (config.responseType === 'stream') {
        response.data = stream;
        settle(resolve, reject, response);
      } else {
        var responseBuffer = [];
        var totalResponseBytes = 0;
        stream.on('data', function handleStreamData(chunk) {
          responseBuffer.push(chunk);
          totalResponseBytes += chunk.length;
          
          if (config.maxContentLength > -1 && totalResponseBytes > config.maxContentLength) {
            
            rejected = true;
            stream.destroy();
            reject(new AxiosError('maxContentLength size of ' + config.maxContentLength + ' exceeded',
              AxiosError.ERR_BAD_RESPONSE, config, lastRequest));
          }
        });
        stream.on('aborted', function handlerStreamAborted() {
          if (rejected) {
            return;
          }
          stream.destroy();
          reject(new AxiosError(
            'maxContentLength size of ' + config.maxContentLength + ' exceeded',