Replace extend() with Object.assign()

gulp/tasks/build.js

@@ -16,7 +16,6 @@ var gulp = require('gulp'),
     uncomment = require('gulp-uncomment'),
     whitespace = require('gulp-whitespace'),
     del = require('del'),
-    extend = require('extend'),
     options = require('../utils/options.js');
 
 // Options to be used in Prepro.js preprocessing through the global __options
@@ -51,7 +50,7 @@ buildNames.forEach(function(name) {
                     // Note that this would be merge in with already existing
                     // objects.
                     return {
-                        __options: extend({}, options, buildOptions[name])
+                        __options: Object.assign({}, options, buildOptions[name])
                     };
                 }
             }))

gulp/utils/options.js

@@ -11,7 +11,6 @@
  */
 
 var execSync = require('child_process').execSync,
-    extend = require('extend'),
     // Require the __options object, so we have access to the version number and
     // make amendments, e.g. the release date.
     options = require('../../src/options.js');

package.json

@@ -47,7 +47,6 @@
   "devDependencies": {
     "acorn": "~0.5.0",
     "del": "^2.2.1",
-    "extend": "^3.0.0",
     "gulp": "^3.9.1",
     "gulp-bump": "^2.2.0",
     "gulp-cached": "^1.1.0",