For some reason Media Entity doesn't have the latest commit:
$ composer update drupal/media_entity
The "composer/installers" plugin requires composer-plugin-api 1.0.0, this *WILL* break in the future and it should be fixed ASAP (require ^1.0 for example).
Loading composer repositories with package information
Updating dependencies (including require-dev)
- Installing drupal/media_entity (dev-8.x-1.x 6b80069)
Cloning 6b80069fb12ff360b020f9d4cdeacbe8f85ad944
Generating optimized autoload files
Maintaining patches
For some reason Media Entity doesn't have the latest commit:
Here's a list of the commits: https://www.drupal.org/node/2099473/commits