Switch the display mode to fullscreen

So the full content can be displayed on a 720p monitor.

Change-Id: Iaf3b7748d8e85c6f6e72c6b37c38de70a3003762
diff --git a/edgetpu_demo b/edgetpu_demo
index bd37bed..c3564ef 100755
--- a/edgetpu_demo
+++ b/edgetpu_demo
@@ -19,7 +19,7 @@
       --filter car,truck \
       --max_area 0.1 \
       --color white \
-      --displaymode window
+      --displaymode fullscreen
 # Disable stream demo for now.
 # elif [[ "$1" == "--stream" ]]; then
 #   echo "Press 'q' to quit."