Fix casing of App_Plugins

[olibos]

Fix #64

Reason: In the method AddRuntimeMinifier:

                return new SmidgeFileProvider(
                    hostEnv.WebRootFileProvider,
                    new GlobPatternFilterFileProvider(
                        hostEnv.ContentRootFileProvider,
                        // only include js or css files within App_Plugins
                        new[] { "/App_Plugins/**/*.js", "/App_Plugins/**/*.css" }));

The Glob Pattern uses /App_plugins/ and globs are case sensitive, which mean your files are filtered out.

To reproduce the error, you only have to change your appsettings :

{
"Umbraco": {
      "Hosting": {
        "Debug": false
      }
  }
}

Based on https://github.com/KevinJump/uSync/blob/v9/main/uSync.Backoffice.Assets/App_Plugins/uSync/package.manifest where All paths starts with:~/App_Plugins/

[enkelmedia]

What a hero! Thanks @olibos! Your contributions has really been helpful in these stressful times =D

https://github.com/enkelmedia/TheDashboard/issues/64