Google has started rolling out a new version of Play Store app. The latest update brings version 4.4.21, which will most probably premiere as part of Android 4.4 KitKat. This new update brings minor UI changes, and prepares your device for the upcoming Newsstand, which will soon replace Magazines.
As the update is getting rolled out in batches, it might take few days or hours to reach on your device. Still if you are eager to use this version of Play Store app, head over to this link to download the apk and install it.
Via - GSMArena