A couple of issues seem to have cropped up since upgrading to the GM Seed of MacOS Sierra, I spent a couple of hours today looking into it, but the only solution was to remove grunticon from the gruntfile
Running "grunticon:build" (grunticon) task
svg-to-png now spawning phantomjs...
(using path: /node_modules/svg-to-png/node_modules/phantomjs/lib/phantom/bin/phantomjs)
Something went wrong with phantomjs...
Fatal error: Command failed: /node_modules/svg-to-png/node_modules/phantomjs/lib/phantom/bin/phantomjs /node_modules/svg-to-png/lib/phantomscript.js
Process finished with exit code 1
A couple of issues seem to have cropped up since upgrading to the GM Seed of MacOS Sierra, I spent a couple of hours today looking into it, but the only solution was to remove grunticon from the gruntfile