Cordova - Plugin and config.xml file

i try to add the splash screen plugin in the res/xml/config.xml file of my project.

This is what i want:

<?xml version='1.0' encoding='utf-8'?>
<widget id="fr.myname.firstapp" version="0.0.1" xmlns="http://ift.tt/18Fk3Vk" xmlns:cdv="http://ift.tt/1cHnIYX" xmlns:gap="http://ift.tt/16o90D3">
<name>FirstApp</name>
<description>
    this is my first app
</description>
<author email="email@example.com" href="http://example.com">
    My name
</author>
<content src="index.html" />
<access origin="*" subdomains="true" />
<preference name="loglevel" value="DEBUG" />
<preference name="SplashScreen" value="screen" />
<preference name="SplashScreenDelay" value="4000" />
<feature name="Notification">
    <param name="android-package" value="org.apache.cordova.dialogs.Notification" />
</feature>
...
</widget>

After the build of the app with "cordova build android" command, the two lines i added have disappeared:

<preference name="SplashScreen" value="screen" />
<preference name="SplashScreenDelay" value="4000" />

What can cause that? i don't understand why it override my changes while i just followed official documentation.

Thanks for your help.