Fix icons cacher regex for compressed output

Signed-off-by: John Molakvoæ (skjnldsv) <skjnldsv@protonmail.com>

Author: skjnldsv

lib/private/Template/IconsCacher.php

@@ -47,7 +47,7 @@ class IconsCacher {
 	protected $urlGenerator;
 
 	/** @var string */
-	private $iconVarRE = '/--(icon-[a-zA-Z0-9-]+): url\(["\']([a-zA-Z0-9-_\~\/\.\?\=]+)[^;]+;/m';
+	private $iconVarRE = '/--(icon-[a-zA-Z0-9-]+):\s?url\(["\']([a-zA-Z0-9-_\~\/\.\?\=]+)[^;]+;/m';
 
 	/** @var string */
 	private $fileName = 'icons-vars.css';