Upgrade to 4. 30 - plugins.txt -> InstalledPlugins.json

I renamed the file plugins.txt to plugins.json, but still get error:
JsonReaderException: Unexpected character encountered while parsing value: P. Path '', line 0, position 0.
...
Nop.Services.Plugins.PluginsInfo.DeserializePluginInfo(string json) in PluginsInfo.cs
Nop.Services.Plugins.PluginsInfo.LoadPluginInfo() in PluginsInfo.cs

You can't just rename the old .txt file.  The format is completely different.  For example:

{
  "InstalledPluginNames": [
    "Obsolete field, using only for compatibility"
  ],
  "InstalledPlugins": [
    {
      "SystemName": "DiscountRequirement.MustBeAssignedToCustomerRole",
      "Version": "1.34"
    },
    {
      "SystemName": "CurrencyExchange.ECB",
      "Version": "1.26"
    },
    {
      "SystemName": "Misc.SendinBlue",
      "Version": "3.26"
    },
    {
      "SystemName": "Payments.CheckMoneyOrder",
      "Version": "1.44"
    },
    {
      "SystemName": "Payments.Manual",
      "Version": "1.53"
    },
    {
      "SystemName": "Payments.PayPalSmartPaymentButtons",
      "Version": "1.13"
    },
    {
      "SystemName": "Payments.PayPalStandard",
      "Version": "1.60"
    },
    {
      "SystemName": "Pickup.PickupInStore",
      "Version": "1.34"
    },
    {
      "SystemName": "Tax.Avalara",
      "Version": "2.35"
    },
    {
      "SystemName": "Tax.FixedOrByCountryStateZip",
      "Version": "1.33"
    },
    {
      "SystemName": "Widgets.FacebookPixel",
      "Version": "1.02"
    },
    {
      "SystemName": "Widgets.GoogleAnalytics",
      "Version": "1.62"
    },
    {
      "SystemName": "Widgets.NivoSlider",
      "Version": "1.38"
    },
    {
      "SystemName": "ExternalAuth.Facebook",
      "Version": "1.63"
    },
    {
      "SystemName": "Shipping.FedEx",
      "Version": "1.36"
    },
    {
      "SystemName": "Shipping.FixedByWeightByTotal",
      "Version": "2.23"
    },
    {
      "SystemName": "Shipping.USPS",
      "Version": "1.47"
    },
    {
      "SystemName": "Shipping.ShipStation",
      "Version": "1.06"
    }
  ],
  "PluginNamesToUninstall": [],
  "PluginNamesToDelete": [],
  "PluginNamesToInstall": []
}