Update composer.json

[oreillysean]

Replace rabbitmq-management-api with a packagist source

Basically this is just a direct copy of the work @andrewmy did! This change is done for all the same reasons the comment here explains, "_A year has passed since richardfullmer/php-rabbitmq-management-api#11 — time to move on and stop using the fork as a custom repo.

This will make all the builds quicker, race-condition free, and avoid the weirdness of using a source repo in a widely used package._"

php-enqueue/enqueue-dev#1238

[andrewmy]

@oreillysean good catch, when doing #1238 I forgot to update the sub-package itself. Please PR this to enqueue-dev repo, this one is a read-only split.

[oreillysean]

@andrewmy thanks I see now the big READ ONLY message on this repo, I'll redo this in the correct place

[andrewmy]

@oreillysean perhaps there are more places to update, would be nice to check :)

[oreillysean]

Will do thanks :)