docs: Remove null example

Author: tony

examples/session-environment.json

@@ -7,7 +7,6 @@
   "windows": [
     {
       "panes": [
-        null, 
 	"./manage.py runserver 0.0.0.0:${SERVER_PORT}"
       ], 
       "window_name": "Django project"

examples/session-environment.yaml

@@ -6,5 +6,4 @@ environment:
 windows:
   - window_name: Django project
     panes:
-    -
     - ./manage.py runserver 0.0.0.0:${SERVER_PORT}