OpenAPI spec task: Load pleroma application to get version info

For whatever reason it seems to pick up the version without loading the
app on my machine, but not on the CI.

lib/mix/tasks/pleroma/openapi_spec.ex

@@ -1,5 +1,7 @@
 defmodule Mix.Tasks.Pleroma.OpenapiSpec do
   def run([path]) do
+    # Load Pleroma application to get version info
+    Application.load(:pleroma)
     spec = Pleroma.Web.ApiSpec.spec(server_specific: false) |> Jason.encode!()
     File.write(path, spec)
   end