Greetings!  When trying to set data in the request to a readable stream, it looks like stream errors aren't being captured and sent back through `reject`. Instead, it just throws.

Pretty simple repo here:

```js
const axios = require('axios');
const fs = require('fs');

axios.post('/to/here', {
    data: fs.createReadStream('/it/dont/exist')
  })
  .then(console.log)
  .catch(console.error)
```

Pretty sure the issue is here:
https://github.com/axios/axios/blob/master/lib/adapters/http.js#L236

The data gets piped without attaching an `.on('error')` handler to reject the promise. 
lib/adapters/http.js
if (!headers['User-Agent'] && !headers['user-agent']) {
      headers['User-Agent'] = 'axios/' + pkg.version;
    }
    if (data && !utils.isStream(data)) {
      if (Buffer.isBuffer(data)) {
        
      } else if (utils.isArrayBuffer(data)) {
        data = new Buffer(new Uint8Array(data));
      } else if (utils.isString(data)) {
        data = new Buffer(data, 'utf-8');
      } else {
        return reject(createError(
          'Data after transformation must be a string, an ArrayBuffer, a Buffer, or a Stream',
          config
        ));
      }
      
      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 parsed = url.parse(config.url);
    var protocol = parsed.protocol || 'http:';