Move to newer base image for end-to-end tests

This updates to Node 14 (current LTS) as well moving from Debian Stretch to
Buster for the base OS. The Debian upgrade brings along a newer Python 3.8,
which is actively supported.

Fixes element-hq/element-web#16272

scripts/ci/Dockerfile

@@ -1,8 +1,7 @@
 # Update on docker hub with the following commands in the directory of this file:
 # docker build -t vectorim/element-web-ci-e2etests-env:latest .
-# docker log
 # docker push vectorim/element-web-ci-e2etests-env:latest
-FROM node:10
+FROM node:14-buster
 RUN apt-get update
 RUN apt-get -y install build-essential python3-dev libffi-dev python-pip python-setuptools sqlite3 libssl-dev python-virtualenv libjpeg-dev libxslt1-dev uuid-runtime
 # dependencies for chrome (installed by puppeteer)