chore(deps): update the replace versions in composer

[phil-davis]

Otherwise, composer update complains.

Update to match what is currently being used in core.

composer was complaining:

$ composer update
[bamarni-bin] The setting "extra.bamarni-bin.forward-command" will be set to "true" from 2.x onwards. If you wish to keep it to "false", you need to set it explicitly.
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - owncloud/files_external_s3 is present at version dev-master and cannot be modified by Composer
    - Root composer.json requires roave/security-advisories dev-latest -> satisfiable by roave/security-advisories[dev-latest].
    - roave/security-advisories dev-latest conflicts with guzzlehttp/guzzle <7.12.1 (owncloud/files_external_s3 dev-master replaces guzzlehttp/guzzle ^7.7).