UILaunchStoryboardName and it's value CDVLaunchScreen is being removed by ionic prepare command

I have a Ionic Cordova project and am trying to make sure that it is fullscreen on iPhone 6 .
I have gone to questions like this one and everything works fine until I run ionic prepare and it removes <key>UILaunchStoryboardName</key><string>CDVLaunchScreen</string> from the .plist file. I tried adding this:

"config_munge": {
"files": {
  "*-Info.plist": {
    "parents": {
      "UILaunchStoryboardName": [
          "xml": "<string>CDVLaunchScreen</string>",
          "count": 1

to my ios.json and that doesn’t help. I also tried this in my config.xml file:

<platform name="ios">
    <config-file parent="UILaunchStoryboardName" target="*-Info.plist">

And that doesn’t help.
all that always gets overwritten with the next ionic prepare command.
How do I prevent that from being overwritten?