package/opencv3: bump version to 3.4.20

Changelog:
https://github.com/opencv/opencv/wiki/OpenCV-Change-Logs-v2.2%E2%80%90v4.10#version3420

Updated license hash due to copyright year bump:
https://github.com/opencv/opencv/commit/7b7774476e92247c801309387df2ea64465976e3

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/opencv3/opencv3.hash

@@ -1,3 +1,3 @@
 # Locally calculated
-sha256  9b913e74299ce4416a5c94000da577c592bf670fd53bad16220eb115a0821529  opencv3-3.4.19.tar.gz
-sha256  c1fed9cd2f557ba23a1b37a21e2c90629d1a60bdb61e92d0e79369bb6fca3390  LICENSE
+sha256  b9eda448a08ba7b10bfd5bd45697056569ebdf7a02070947e1c1f3e8e69280cd  opencv3-3.4.20.tar.gz
+sha256  3f221dbe2ca9228d6470990ed28e55957e8506335df4620539c4db0dd27a6b4c  LICENSE

package/opencv3/opencv3.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-OPENCV3_VERSION = 3.4.19
+OPENCV3_VERSION = 3.4.20
 OPENCV3_SITE = $(call github,opencv,opencv,$(OPENCV3_VERSION))
 OPENCV3_INSTALL_STAGING = YES
 OPENCV3_LICENSE = BSD-3-Clause