chore(build): replace deprecated gulp-rimraf by node del

see
https://github.com/gulpjs/gulp/blob/0bb073de4418200e95bd56e0e06ac9d5fc5723b2/docs/recipes
/delete-files-folder.md

gulpfile.js

@@ -1,4 +1,5 @@
 var benchpress = require('angular-benchpress/lib/cli');
+var del = require('del');
 var es = require('event-stream');
 var file2moduleName = require('./file2modulename');
 var fs = require('fs');
@@ -109,9 +110,8 @@ var sourceTypeConfigs = {
 };
 
 
-gulp.task('modules/clean', function() {
-  return gulp.src('build', {read: false})
-      .pipe($.rimraf());
+gulp.task('modules/clean', function(cb) {
+  del('build', cb);
 });
 
 gulp.task('modules/build.dart/src', function() {

package.json

@@ -9,11 +9,11 @@
   "license": "Apache-2.0",
   "dependencies": {
     "angular-benchpress": "^0.1.3",
+    "del": "~1",
     "es6-module-loader": "^0.9.2",
     "event-stream": "^3.1.5",
     "glob": "^4.0.6",
     "gulp-connect": "~1.0.5",
-    "gulp-rimraf": "^0.1.0",
     "karma": "^0.12.23",
     "karma-chrome-launcher": "^0.1.4",
     "karma-cli": "^0.0.4",