Update submodule sonic-py-swsssdk, including below commits:

a83366e 2020-06-08 | Upgrade redis library to 3.5.3 (sonic-net#80) [Qi Luo]
800a8a8 2020-06-08 | Add missing dependency (sonic-net#76) [Qi Luo]
132f8d5 2020-05-26 | [MultiDB]: use python class composition to avoid confusion in base class (sonic-net#74) [Dong Zhang]

Author: qiluo-msft

files/build_templates/sonic_debian_extension.j2

@@ -104,7 +104,7 @@ sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install $CONFIG
 sudo rm -rf $FILESYSTEM_ROOT/$CONFIG_ENGINE_WHEEL_NAME
 
 # Install Python client for Redis
-sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install "redis==2.10.6"
+sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install "redis==3.5.3"
 
 # Install redis-dump-load Python 3 package
 # Note: the scripts will be overwritten by corresponding Python 2 package