Travis and "Could not authenticate against github.com"

[nicosomb]

We have problems with some PR (for example this one #1615), TravisCI returns this error:

Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Installing paragonie/random_compat (v1.2.0)
    Downloading
    Failed to download paragonie/random_compat from dist: Could not authenticate against github.com
    Now trying to download from source
  - Installing paragonie/random_compat (v1.2.0)
    Cloning b0e69d10852716b2ccbdff69c75c477637220790
  - Removing symfony/polyfill-php70 (v1.0.1)
  - Installing symfony/polyfill-php70 (v1.1.0)
    Downloading                                         
  [Composer\Downloader\TransportException]   
  Could not authenticate against github.com  

We need to have a look to this Symfony PR https://github.com/symfony/symfony/pull/17171/files to apply these changes too.