Versions >= 3.1.0 of grunt-spritesmith supported
Versions >= 3.1.0 of grunt-spritesmith supported

Since version 3.1.0 grunt-newer is supported by grunt-spritesmith.

see https://github.com/Ensighten/grunt-spritesmith/blob/master/CHANGELOG.md
mattkime/grunt-newr,tschaub/grunt-newer