move grunt uglify to devDependencies

Author: guybedford

package.json

@@ -64,7 +64,6 @@
   },
   "dependencies": {
     "6to5-core": "~3.5.3",
-    "grunt-contrib-uglify": "0.6.0",
     "traceur": "0.0.82",
     "when": "^3.7.2"
   }