Travis-CI: Return back to Ubuntu

.travis.yml

@@ -1,21 +1,8 @@
-language: nix
-
-cache:
-  directories:
-  - $HOME/nix.store
-
-before_cache:
-  - mkdir -p $HOME/nix.store
-  - nix copy --to file://$HOME/nix.store -f default.nix buildInputs
+dist: bionic
 
 before_install:
-  - sudo mkdir -p /etc/nix
-  - echo "substituters = https://cache.nixos.org/ file://$HOME/nix.store" | sudo tee -a /etc/nix/nix.conf > /dev/null
-  - echo 'require-sigs = false' | sudo tee -a /etc/nix/nix.conf > /dev/null
-
-before_script:
-  # Make sure that version is up-to-date
-  - sed -i "s/version = .*/version = \"$(git describe --abbrev=0 --tags | sed 's/v//')\";/" default.nix
+  - sudo apt update
+  - sudo apt install texlive-full rubber pandoc
 
 script:
-  - nix-build --option sandbox true
+  - make