doc: fix a typo in the assert.md

PR-URL: https://github.com/nodejs/node/pull/9598
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/assert.md

@@ -271,7 +271,7 @@ assert.notDeepEqual(obj1, obj3);
   // AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
 
 assert.notDeepEqual(obj1, obj4);
-  // OK, obj1 and obj2 are not deeply equal
+  // OK, obj1 and obj4 are not deeply equal
 ```
 
 If the values are deeply equal, an `AssertionError` is thrown with a `message`