When installing balena-etcher via apt on Debian/Ubuntu,
the command `balena-etcher-electron` fails with the error:
line 3: /usr/bin/balena-etcher-electron.bin: No such file or directory
This is because the /usr/bin/balena-etcher-electron is a symlink
to /opt/balenaEtcher/balena-etcher-electron, but the script looks
for balena-etcher-electron.bin in the symlink directory, not the
actual script location directory.
This commit uses `$(dirname "$(readlink -f "${BASH_SOURCE[0]}")")` to
find the real location of the balena-etcher-electron script without
symlink, so that balena-etcher-electron.bin is correctly found.
Change-Type: patch
Changelog-Entry: Fix error when launching from terminal when installed via apt.
Fixes: https://github.com/balena-io/etcher/issues/3074
