Fix "modify_autojump_sh" wrong behavior

The "modify_autojump_sh" function in "install.py" patches the "autojump.sh" in the wrong way in case the user has chosen a different dest_dir.
In particular, if we consider a dest_dir set to "/usr/local/Cellar/autojump/22.2.2", it would write something like:
source /usr/local/Cellar/autojump/22.2.2/etc/profile.d/autojump.${shell}
which does not exist, since all the autojump.${shell} files are placed under the share_dir. The correct path would be:
/usr/local/Cellar/autojump/22.2.2/share/autojump/autojump.${shell}