Moved to Node.js >= 8 for async/await support

Author: twolfson

package.json

@@ -24,7 +24,7 @@
   "main": "grunt.js",
   "bin": "bin/grunt-zip",
   "engines": {
-    "node": ">= 0.10.0"
+    "node": ">= 8.0.0"
   },
   "scripts": {
     "test": "rm -r test/actual &> /dev/null && mocha"