Fix incorrect parameter for `$wp_filesystem->chmod()`

I got an error when I run `git add .` for my plugin like below.

```
$ git add .
error: open("bin/install-wp-tests.sh"): Permission denied
error: unable to index file bin/install-wp-tests.sh
fatal: adding files failed
```

Because second parameter of `$wp_filesystem->chmod()` was not correct.

## Before Fix

```
$ ls -alF bin/
total 8
drwxr-xr-x  3 miyauchi  staff   102 11 23 02:08 ./
drwxr-xr-x  8 miyauchi  staff   272 11 23 02:08 ../
--wxrw--wt  1 miyauchi  staff  2137 11 23 02:08 install-wp-tests.sh*
```

## After Fix

```
$ ls -alF bin/
total 8
drwxr-xr-x  3 miyauchi  staff   102 11 23 02:08 ./
drwxr-xr-x  8 miyauchi  staff   272 11 23 02:08 ../
-rwxr-xr-x  1 miyauchi  staff  2137 11 23 02:08 install-wp-tests.sh*
```