fix: __proto__ copy

.travis.yml

@@ -1,11 +1,13 @@
-sudo: false
+
 language: node_js
 node_js:
   - '4'
   - '6'
   - '7'
+before_install:
+  - npm i npminstall -g
 install:
-  - npm i npminstall && npminstall
+  - npminstall
 script:
   - npm run ci
 after_script:

appveyor.yml

@@ -11,6 +11,6 @@ install:
 test_script:
   - node --version
   - npm --version
-  - npm run ci
+  - npm run test
 
 build: off

index.js

@@ -54,7 +54,7 @@ module.exports = function extend() {
       if (target === copy) continue;
 
       // Recurse if we're merging plain objects
-      if (deep && copy && isPlainObject(copy)) {
+      if (deep && copy && isPlainObject(copy) && target.constructor !== Object) {
         clone = src && isPlainObject(src) ? src : {};
         // Never move original objects, clone them
         target[name] = extend(deep, clone, copy);

test/index.js

@@ -619,3 +619,13 @@ test('works without Array.isArray', function (t) {
   Array.isArray = savedIsArray;
   t.end();
 });
+
+test('fix __proto__ copy', function (t) {
+  var r = extend(true, {}, JSON.parse('{"__proto__": {"polluted": "yes"}}'));
+  t.deepEqual(
+    JSON.stringify(r),
+    '{}',
+    'It should not copy __proto__'
+  );
+  t.end();
+});