CI: Install STIX fonts for TeX-math

Change-Id: I96468b0a89301b5d532228bfa6f45d7e0ec9b2d1
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 3f89b0f..d55e8f1 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -25,7 +25,7 @@
 
     - start_section install_linux_packages "Installing missing Linux packages"
     - apt-get update
-    - apt-get install -y libvulkan1 libu2f-udev fonts-liberation build-essential libglpk40 libcurl4-gnutls-dev libxml2-dev libsodium-dev libsecret-1-dev libfontconfig1-dev libssl-dev libxt6 libpq-dev imagemagick inkscape scour poppler-utils
+    - apt-get install -y libvulkan1 libu2f-udev fonts-liberation build-essential libglpk40 libcurl4-gnutls-dev libxml2-dev libsodium-dev libsecret-1-dev libfontconfig1-dev libssl-dev libxt6 libpq-dev imagemagick inkscape scour poppler-utils fonts-stix
     - wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
     - dpkg -i google-chrome-stable_current_amd64.deb || apt-get install -y -f
 #    - wget http://mirror.cs.uchicago.edu/google-chrome/pool/main/g/google-chrome-stable/google-chrome-stable_${CHROME_VERSION}_amd64.deb