test: fix the arguments order in assert.strictEqual

I working at "Code and Learn" on Node fest 2018 in Japan.

Refs: nodejs#24431

test/parallel/test-fs-write-string-coerce.js

@@ -17,12 +17,12 @@ fs.open(fn, 'w', 0o644, common.mustCall(function(err, fd) {
  fs.write(fd, data, 0, 'utf8', common.mustCall(function(err, written) {
  console.log('write done');
  assert.ifError(err);
- assert.strictEqual(Buffer.byteLength(expected), written);
+ assert.strictEqual(written, Buffer.byteLength(expected));
  fs.closeSync(fd);
  const found = fs.readFileSync(fn, 'utf8');
  console.log(`expected: "${expected}"`);
  console.log(`found: "${found}"`);
  fs.unlinkSync(fn);
- assert.strictEqual(expected, found);
+ assert.strictEqual(found, expected);
  }));
 }));