code being changed after saving

Hey,

I running a small section of code using your plugin, however for some reason I add code, but when I click save it has changed my code and removed a “\” character

This is my code

preg_replace('/\s+/', '', $postcode);

but it changes it to:

preg_replace('/s+/', '', $postcode);

Any ideas why the plugin would be ignoring the \ in /\s+/ ?

https://wordpress.org/plugins/custom-css-js-php/