test: fix the arguments order in assert.strictEqual

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

Refs: nodejs#24431

Author: sigwyg

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);
   }));
 }));