[Refactor] switching to a maintained Object.assign package

Author: ljharb

assert.js

@@ -34,8 +34,8 @@ const AssertionError = require('./internal/assert/assertion_error');
 const { inspect } = require('util/');
 const { isPromise, isRegExp } = require('util/').types;
 
-const objectAssign = Object.assign ? Object.assign : require('es6-object-assign').assign;
-const objectIs = Object.is ? Object.is : require('object-is');
+const objectAssign = require('object.assign/polyfill')();
+const objectIs = require('object-is/polyfill')();
 
 const RegExpPrototypeTest = require('call-bind/callBound')('RegExp.prototype.test');
 

package.json

@@ -38,9 +38,9 @@
   },
   "dependencies": {
     "call-bind": "^1.0.2",
-    "es6-object-assign": "^1.1.0",
     "is-nan": "^1.2.1",
     "object-is": "^1.0.1",
+    "object.assign": "^4.1.4",
     "util": "^0.12.0"
   }
 }