test: refactor domain test

Use assert.strictEqual() instead of assert.equal().

PR-URL: nodejs#10269
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-domain-stack-empty-in-process-uncaughtexception.js

@@ -7,13 +7,14 @@ const assert = require('assert');
 const d = domain.create();
 
 process.on('uncaughtException', common.mustCall(function onUncaught() {
-  assert.equal(process.domain, null,
-               'domains stack should be empty in uncaughtException handler');
+  assert.strictEqual(process.domain, null,
+                     'domains stack should be empty in uncaughtException' +
+                     ' handler');
 }));
 
 process.on('beforeExit', common.mustCall(function onBeforeExit() {
-  assert.equal(process.domain, null,
-               'domains stack should be empty in beforeExit handler');
+  assert.strictEqual(process.domain, null,
+                     'domains stack should be empty in beforeExit handler');
 }));
 
 d.run(function() {