Move git sha to proper .env file

Author: mcabrams

{{ cookiecutter.project_slug }}/.env.example

@@ -1,4 +1,3 @@
 COMPOSE_PROJECT_NAME={{ cookiecutter.project_slug }}
-GIT_SHA=foobarxyz
 # FILL THESE IN:
 # SENTRY_DSN=

{{ cookiecutter.project_slug }}/server/.env

@@ -3,3 +3,4 @@ DJANGO_ALLOWED_HOSTS=localhost,server
 DJANGO_CORS_ORIGIN_WHITELIST=http://localhost:8080,http://client:8080
 DJANGO_TRUSTED_ORIGINS=http://localhost:8080,http://client:8080
 REDIS_URL=redis://redis:6379/0
+GIT_SHA=foobarxyz