Apple has today released iOS 8.4.1 to the public. This comes one month after the release of 8.4. This update only went through two betas before release. iOS 8.4.1 brings improvements and fixes to Apple Music and not much else.
This is a rather small update, coming in at only 57.4 MB on an iPhone 6 running 8.4. You can update in Settings > General > Software update > iOS 8.4.1.