use GH actions instead of Travis

.github/workflows/ci.yml

@@ -0,0 +1,21 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: cachix/install-nix-action@v13
+
+      # - uses: cachix/cachix-action@v10
+      #   with:
+      #     name: noredink-ui
+      #     authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      #     extraPullNames: niv
+
+      - run: nix-shell --pure --run 'shake --verbose ci'

.travis.yml

@@ -1,54 +0,0 @@
-language: nix
-
-env:
-  global:
-    - CACHIX_CACHE=noredink-ui
-
-cache:
-  directories:
-    - node_modules
-    - ~/.elm
-
-install:
-  # This setup script comes from the cachix docs[1], but we annotate it here so
-  # it's easier to maintain.
-  #
-  # [1]: https://docs.cachix.org/continuous-integration-setup/travis-ci.html
-
-  # First, we need to tell Nix that the current user is trusted to make changes to
-  # the system configuration, so that we can do exactly that in the next step.
-  - echo "trusted-users = $USER" | sudo tee -a /etc/nix/nix.conf
-  - sudo systemctl restart nix-daemon
-
-  # Next, we need to tell Nix to use our cache to avoid building fresh every time.
-  # Under the covers, this means trusting the signing key and adding the
-  # our-cache-name.cachix.org as a substituter. But we don't really need to worry
-  # a lot about the mechanism here, since the `cachix use` statement here will
-  # take care of everything for us if it has the right permissions.
-  - nix-env -iA nixpkgs.cachix
-  - cachix use $CACHIX_CACHE
-
-  # Next, we list all the paths that Nix currently knows about so that we don't
-  # waste time trying to push them later.
-  - nix path-info --all > /tmp/store-path-pre-build
-
-  # Finally, we run `nix-shell` with a no-op command to download our real
-  # dependencies. This step should now take advantage of the cachix cache and
-  # avoid rebuilding any upstream software we depend on! (At the time of this
-  # writing, that measn we avoid compiling `niv` and `elm-forbid-import` on every
-  # run.)
-  #
-  # Note that this step is technically not necessary--running our build command in
-  # `nix-shell` below would also take care of this--but getting dependencies here
-  # lets us collapse the (huge) download list in the Travis UI.
-  - nix-shell --run 'true'
-
-script:
-  - nix-shell --pure --run 'shake --verbose ci'
-
-after_success:
-  # After we successfully build, we want to cache whatever we can. That means that
-  # when dependencies change, we should only build them once. The invocation below
-  # just gets the difference between the derivations we had before the build and
-  # the derivations we have now, and pushes the new ones.
-  - comm -13 <(sort /tmp/store-path-pre-build | grep -v '\.drv$') <(nix path-info --all | grep -v '\.drv$' | sort) | cachix push $CACHIX_CACHE