WordPress Multisite Image URL Not Masked

Hi guys,

I have a clean installation of WordPress 4.0 with Multisite (Subdomain).

My question is, why is the image url on my child site is:
https://childsite.mainsite.com/wp-content/uploads/sites/2014/09/image.png

I thought it is suppose to be:
https://childsite.mainsite.com/files/2014/09/image.png

This is a link to my child site:
https://pid.malaysiadesignagency.com

As you can see the image url of the “Hello World” post is not masked to “files”

This is my htacess fil:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
</IfModule>

# END WordPress

Thank you.