test: cleanup test-fs-watch.js

Reversed "actual" and "expected" arguments for assert.strictEqual().

Replaced constructor with regular expression for assert.throws().

PR-URL: nodejs/node#12595
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Bryan English <bryan@bryanenglish.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/sequential/test-fs-watch.js

@@ -82,7 +82,7 @@ assert.doesNotThrow(
  function() {
  const watcher = fs.watch(testsubdir, function(event, filename) {
  const renameEv = common.isSunOS || common.isAix ? 'change' : 'rename';
- assert.strictEqual(renameEv, event);
+ assert.strictEqual(event, renameEv);
  if (expectFilePath) {
  assert.strictEqual(filename, 'newfile.txt');
  } else {