test: add missing assert.deepEqual() test case

None of the existing tests checked for the situation where
`assert.deepEqual()` receives two objects that have the same number of
keys but different key names. Therefore, line 242 of `lib/assert.js` was
not being exercised by any tests.

This change adds the missing test case.

PR-URL: https://github.com/nodejs/node/pull/8152
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-assert.js

@@ -165,6 +165,9 @@ assert.doesNotThrow(makeBlock(a.deepEqual, new Number(1), {}),
 assert.doesNotThrow(makeBlock(a.deepEqual, new Boolean(true), {}),
                     a.AssertionError);
 
+// same number of keys but different key names
+assert.throws(makeBlock(a.deepEqual, {a: 1}, {b: 1}), a.AssertionError);
+
 //deepStrictEqual
 assert.doesNotThrow(makeBlock(a.deepStrictEqual, new Date(2000, 3, 14),
                     new Date(2000, 3, 14)),