add default ACTIVITY_PUB=false to .env.example

.env.example

@@ -53,3 +53,6 @@ MIX_PUSHER_APP_CLUSTER="${PUSHER_APP_CLUSTER}"
 MIX_APP_URL="${APP_URL}"
 MIX_API_BASE="${API_BASE}"
 MIX_API_SEARCH="${API_SEARCH}"
+
+ACTIVITY_PUB=false
+