build: copy entries in static folder in to config.build.assetsRoot

fixed vuejs-templates#208

Author: UncleBill

template/build/build.js

@@ -20,7 +20,7 @@ spinner.start()
 var assetsPath = path.join(config.build.assetsRoot, config.build.assetsSubDirectory)
 rm('-rf', assetsPath)
 mkdir('-p', assetsPath)
-cp('-R', 'static/', assetsPath)
+cp('-R', 'static/', config.build.assetsRoot)
 
 webpack(webpackConfig, function (err, stats) {
   spinner.stop()