Add install of matplotlib to raspberry pi disk image

Had to increase the disk image size to support this.  Looks like it requires
at least 2.4 GB.  I moved it to 3 GB to give some extra buffer-- not sure
if there are any issues with this size.

Change-Id: I736ee915b72b5eadb55df270884fe6ce3ea9bef3
diff --git a/y2020/vision/rootfs/target_configure.sh b/y2020/vision/rootfs/target_configure.sh
index f761e84..63a7378 100755
--- a/y2020/vision/rootfs/target_configure.sh
+++ b/y2020/vision/rootfs/target_configure.sh
@@ -38,6 +38,7 @@
   libopencv-videostab3.2 \
   libopencv-viz3.2 \
   python3-opencv \
+  python3-matplotlib \
   gstreamer1.0-plugins-bad \
   gstreamer1.0-plugins-base \
   gstreamer1.0-plugins-good \