Add missing newlines to the generated `default_env.tres` in new projects

This prevents unnecessary whitespace changes in VCS diffs when saving
a scene for the first time in a new project.

editor/project_manager.cpp

@@ -482,7 +482,9 @@ private:
 							set_message(TTR("Couldn't create project.godot in project path."), MESSAGE_ERROR);
 						} else {
 							f->store_line("[gd_resource type=\"Environment\" load_steps=2 format=2]");
+							f->store_line("");
 							f->store_line("[sub_resource type=\"ProceduralSky\" id=1]");
+							f->store_line("");
 							f->store_line("[resource]");
 							f->store_line("background_mode = 2");
 							f->store_line("background_sky = SubResource( 1 )");