I've tried to do what mentioned in this link and I entered this code :
echo "foreign-architecture i386" | sudo tee /etc/dpkg/dpkg.cfg.d/multiarch sudo chmod 644 /etc/dpkg/dpkg.cfg.d/multiarch
Now I see this error.
Unknown configuration key foreign-architecture) found in your (dpkg) configuration files. This warning will become a hard error at a later date, so please remove the offending configuration options and replace them with (dpkg --add-architecture) invocations at the command line.