test: fix pummel/test-crypto-dh, pummel/test-dh-regr

Forgotten in the switch to buffers as the default output in 3570f20.

Fixes #4188.

test/pummel/test-crypto-dh.js

@@ -66,5 +66,5 @@ for (var name in hashes) {
   group2.generateKeys();
   var key1 = group1.computeSecret(group2.getPublicKey());
   var key2 = group2.computeSecret(group1.getPublicKey());
-  assert.equal(key1, key2);
+  assert.deepEqual(key1, key2);
 }

test/pummel/test-dh-regr.js

@@ -33,7 +33,7 @@ for (var i = 0; i < 2000; i++) {
   a.generateKeys();
   b.generateKeys();
 
-  assert.equal(
+  assert.deepEqual(
     a.computeSecret(b.getPublicKey()),
     b.computeSecret(a.getPublicKey()),
     'secrets should be equal!'