Update Dockerfile

Dockerfile

@@ -11,15 +11,7 @@ RUN /opt/netbox/venv/bin/pip3 install pip==20.0.2 && \
     /opt/netbox/venv/bin/pip3 install . && \
     rm -rf /tmp/napalm-onyx
 
-ENV USER=netbox
-ENV UID=1000
-
-RUN adduser \
-    --disabled-password \
-    --gecos "" \
-    --ingroup "$USER" \
-    --uid "$UID" \
-    "$USER"
+RUN adduser --disabled-password --gecos "" --uid "1000" "netbox"
 
 USER netbox
 RUN SECRET_KEY="dummy" /opt/netbox/venv/bin/python /opt/netbox/netbox/manage.py collectstatic --no-input