tests: Switch from Travis to GitHub Actions (faster)

Primary motivation for this is speed: GitHub Actions doesn't limit the
number of concurrent jobs to 4, and also provides a docker registry
(GitHub Packages) that we can use to cache the image (building the image
takes cca 5 minutes, fetching it would take less than 10 seconds). This
is done in another commit.

The workflow definition is a bit more complicated because coveralls
support for GitHub Actions is less mature than for Travis CI, so we need
to manually tell coveralls that all parallel builds have finished and
that it can publish the combined result. Also, coveralls-python support
is work-in-progress
(TheKevJames/coveralls-python#227) so I've
tagged a working snapshot of that PR in my fork. Once it's in a released
version of coveralls-python I'll switch to it.

.github/workflows/tests.yaml

@@ -0,0 +1,36 @@
+name: tests
+on: [push, pull_request]
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - TASK_VERSION: v2.4.0
+          - TASK_VERSION: v2.4.1
+          - TASK_VERSION: v2.4.2
+          - TASK_VERSION: v2.4.3
+          - TASK_VERSION: v2.4.4
+          - TASK_VERSION: v2.5.0
+          - TASK_VERSION: v2.5.1
+    continue-on-error: ${{ matrix.continue-on-error == true }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Prepare docker image
+        run: docker-compose build --build-arg TASK_VERSION=${{ matrix.TASK_VERSION }} tests
+      - name: Test
+        run: make test PYTEST_FLAGS="-n8"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          COVERALLS_PARALLEL: true
+
+  coveralls-finished:
+    needs: tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: Finished
+        uses: coverallsapp/github-action@v1.1.1
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          parallel-finished: true

Dockerfile

@@ -80,7 +80,8 @@ RUN set -ex \
     gcc \
     musl-dev \
  && pip install \
-    coverage coveralls \
+    coverage \
+    https://github.com/liskin/coveralls-python/archive/ea93b7c62d7705e9cc593ae523c89015c4653905.zip \
     pytest \
     pytest-xdist \
     https://github.com/liskin/vimrunner-python/archive/8c19ff88050c09236e7519425bfae33c687483df.zip \

Makefile

@@ -11,7 +11,7 @@ pytest:
 cover-pytest: pytest
 	coverage combine
 	coverage report
-	if [ "$$TRAVIS" ]; then coveralls; fi
+	if [ "$$GITHUB_ACTIONS" ]; then coveralls || :; fi
 
 xvfb-%:
 	xvfb-run --server-args=-noreset $(MAKE) $*

README.md

@@ -3,7 +3,7 @@
 _Proper project management in vim.
 Standing on the shoulders of vimwiki and Taskwarrior_
 
-[![Travis build status](https://travis-ci.org/tbabej/taskwiki.svg?branch=master)](https://travis-ci.org/tbabej/taskwiki)
+[![GitHub Actions build status](https://github.com/tbabej/taskwiki/workflows/tests/badge.svg?branch=master)](https://github.com/tbabej/taskwiki/actions)
 [![Coverage Status](https://coveralls.io/repos/tbabej/taskwiki/badge.svg?branch=master)](https://coveralls.io/r/tbabej/taskwiki?branch=master)
 [![Code Health](https://landscape.io/github/tbabej/taskwiki/master/landscape.svg?style=flat)](https://landscape.io/github/tbabej/taskwiki/master)
 [![Chat with developers](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/tbabej/taskwiki)
@@ -295,7 +295,7 @@ need to install and enable either the `en_US` or `en_GB` locale. For example:
 
     LANG=en_US python -m pytest
 
-Finally you might want to have a look at [the travis configuration](.travis.yml)
+Finally you might want to have a look at [the CI configuration](.github/workflows/tests.yaml)
 and consider using a virtual machine or [Xvfb](https://www.x.org/releases/X11R7.6/doc/man/man1/Xvfb.1.xhtml).
 
 #### Known issues

docker-compose.yml

@@ -10,8 +10,12 @@ services:
     tty: true
     command: make xvfb-cover-pytest
     environment:
+      COVERALLS_PARALLEL:
+      GITHUB_ACTIONS:
+      GITHUB_HEAD_REF:
+      GITHUB_REF:
+      GITHUB_RUN_ID:
+      GITHUB_RUN_NUMBER:
+      GITHUB_SHA:
+      GITHUB_TOKEN:
       PYTEST_FLAGS: "-o cache_dir=/tmp/pytest-cache ${PYTEST_FLAGS:-}"
-      TRAVIS:
-      TRAVIS_JOB_ID:
-      TRAVIS_BRANCH:
-      TRAVIS_PULL_REQUEST: