Apparently WebGL does not play nicely with Travis CI.

.travis.yml

@@ -1,17 +0,0 @@
-language: generic
-dist: xenial
-services:
-  - xvfb
-addons:
-  firefox: latest
-before_install:
-  - sudo apt-get install -y python3-pillow python3-numpy python3-pip
-  - sudo pip3 install selenium
-install:
-  - wget https://github.com/mozilla/geckodriver/releases/download/v0.24.0/geckodriver-v0.24.0-linux64.tar.gz
-  - tar -xf geckodriver-v0.24.0-linux64.tar.gz
-  - sudo mv geckodriver /usr/local/bin
-jobs:
-  include:
-    - stage: test
-      script: xvfb-run -a python3 tests/run_tests.py