The issue is that Ubuntu 17.10 uses Wayland as the default desktop session - which unlike traditional X-Windows desktops, does not invoke a user's login shell (or in fact any shell).
The recommended workaround from Initiatives/Wayland/Session Start GNOME Wiki is given as follows:
The simplest way to set environment variables for a single user under
systemd (version 233 or later), is to create a
.conf file in
~/.config/environment.d, containing lines of the form
the environment.d documentation for more details.
GDM also supports the
/usr/share/gdm/env.d/ drop-in directory. Files
dropped in there also contain lines of the form
NAME=VAL. These affect
all users of the system.
For additional discussion see the article GNOME, Wayland, and environment variables.