test: change call to deprecated util.isError()

common.Error() is just util.isError() which is deprecated. Use
assert.throws() instead.

PR-URL: #3084
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

test/parallel/test-tty-stdout-end.js

@@ -1,16 +1,15 @@
 'use strict';
 // Can't test this when 'make test' doesn't assign a tty to the stdout.
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
+const assert = require('assert');
 
-var exceptionCaught = false;
-
-try {
+const shouldThrow = function() {
   process.stdout.end();
-} catch (e) {
-  exceptionCaught = true;
-  assert.ok(common.isError(e));
-  assert.equal('process.stdout cannot be closed.', e.message);
-}
+};
+
+const validateError = function(e) {
+  return e instanceof Error &&
+    e.message === 'process.stdout cannot be closed.';
+};
 
-assert.ok(exceptionCaught);
+assert.throws(shouldThrow, validateError);