add ncp package

Author: rbrtsmith

package.json

@@ -7,7 +7,7 @@
     "lint": "stylelint '*/**/*.scss' --syntax scss",
     "sass": "node-sass --output-style compressed --include-path ./nebula-css/ -o demo/dist demo/scss/main.scss",
     "autoprefixer": "postcss -u autoprefixer --autoprefixer.browsers 'last 2 versions' 'ie 9-11' -r demo/dist/main.css",
-    "build": "npm run lint && npm run sass && npm run autoprefixer && cp -r demo/assets/ demo/dist/assets",
+    "build": "npm run lint && npm run sass && npm run autoprefixer && ncp demo/assets/ demo/dist/assets",
     "start": "npm run build && onchange '*/**/*.scss' -- npm run build",
     "serve": "http-server demo",
     "test": "npm run lint"
@@ -33,6 +33,7 @@
   "devDependencies": {
     "autoprefixer": "^6.3.5",
     "http-server": "^0.9.0",
+    "ncp": "^2.0.0",
     "node-sass": "^3.4.2",
     "onchange": "^2.2.0",
     "postcss-cli": "^2.5.1",