[swsssdk-py] submodule update for sonic-py-swsssdk (sonic-net#3808)

update multiDB changes in sonic-py-swsssdk, including:
*[multi-DB] Part 4: add sonic-db-cli to replace redis-cli (#54)
*[multi-DB] Part 3: Python API changes (#52)
*remove SonicV2Connector which is not used any more (#53)