test: improve domain-top-level-error-handler-throw

Use assert.strictEqual instead of assert.equal.

PR-URL: https://github.com/nodejs/node/pull/9950
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-domain-top-level-error-handler-throw.js

@@ -48,8 +48,8 @@ if (process.argv[2] === 'child') {
       var expectedExitCode = 7;
       var expectedSignal = null;
 
-      assert.equal(exitCode, expectedExitCode);
-      assert.equal(signal, expectedSignal);
+      assert.strictEqual(exitCode, expectedExitCode);
+      assert.strictEqual(signal, expectedSignal);
     });
   }
 }