update lib to support ES5 polyfills.

Author: opiepj

index.js

@@ -1,25 +1,5 @@
 var exec = require('child_process').exec;
 
-Object.assign = function (target) {
-  'use strict';
-  if (target === undefined || target === null) {
-    throw new TypeError('Cannot convert undefined or null to object');
-  }
-
-  var output = Object(target);
-  for (var index = 1; index < arguments.length; index++) {
-    var source = arguments[index];
-    if (source !== undefined && source !== null) {
-      for (var nextKey in source) {
-        if (source.hasOwnProperty(nextKey)) {
-          output[nextKey] = source[nextKey];
-        }
-      }
-    }
-  }
-  return output;
-};
-
 function puts(error, stdout, stderr) {
   console.log(stdout);
 }
@@ -29,7 +9,15 @@ function WebpackShellPlugin(options) {
     onBuildStart: [],
     onBuildEnd: []
   };
-  this.options = Object.assign(defaultOptions, options);
+  if (!options.onBuildStart) {
+    options.onBuildStart = defaultOptions.onBuildStart;
+  }
+
+  if(!options.onBuildEnd) {
+    options.onBuildEnd = defaultOptions.onBuildEnd;
+  }
+
+  this.options = options;
 
 }