update package.xml

Author: Hanashi

package.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<package xmlns="http://www.woltlab.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.woltlab.com http://www.woltlab.com/XSD/5.4/package.xsd" name="dev.hanashi.wsc.steam-api">
+<package xmlns="http://www.woltlab.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.woltlab.com http://www.woltlab.com/XSD/6.0/package.xsd" name="dev.hanashi.wsc.steam-api">
 	<packageinformation>
 		<!-- dev.hanashi.wsc.steam-api -->
 		<packagename>Steam API</packagename>