iOS App Icon Stretched
If you want to target only iOS 7, you just need 76 x 76, >120 x 120 and 152 x 152 icon sizes.
  If you want to target also iOS 6, you’ll need 57 x 57, 72 x >72, 76 x 76, 114 x 114, 120 x
  120, 144 x 144 and 152 x 152 icon sizes. Without >counting Spotlight and Settings icon if
  you don’t want the OS to interpolate them!


If you change the resolution of the app icons the problem should be fixed.  

Source: http://blog.manbolo.com/2013/08/15/new-metrics-for-ios-7-app-icons