Use GitHub actions for continuous integration (CI)

Bye bye Travis CI, you've served us well.

Author: clue

.gitattributes

@@ -1,6 +1,6 @@
 /.gitattributes export-ignore
+/.github/workflows/ export-ignore
 /.gitignore export-ignore
-/.travis.yml export-ignore
 /examples/ export-ignore
 /phpunit.xml.dist export-ignore
 /phpunit.xml.legacy export-ignore

.github/workflows/ci.yml

@@ -0,0 +1,42 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  PHPUnit:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php:
+          - 7.4
+          - 7.3
+          - 7.2
+          - 7.1
+          - 7.0
+          - 5.6
+          - 5.5
+          - 5.4
+          - 5.3
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+      - run: composer install
+      - run: vendor/bin/phpunit --coverage-text
+        if: ${{ matrix.php >= 7.3 }}
+      - run: vendor/bin/phpunit --coverage-text -c phpunit.xml.legacy
+        if: ${{ matrix.php < 7.3 }}
+
+  PHPUnit-hhvm:
+    name: PHPUnit (HHVM)
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+      - run: curl -O https://dl.hhvm.com/ubuntu/pool/main/h/hhvm/hhvm_3.30.9-1~bionic_amd64.deb
+      - run: sudo apt install -y --allow-downgrades ./hhvm_3.30.9-1~bionic_amd64.deb
+      - run: hhvm $(which composer) install
+      - run: hhvm vendor/bin/phpunit --coverage-text

.travis.yml

@@ -1,4 +1,6 @@
-# clue/reactphp-flux [![Build Status](https://travis-ci.org/clue/reactphp-flux.svg?branch=master)](https://travis-ci.org/clue/reactphp-flux)
+# clue/reactphp-flux
+
+[![CI status](https://github.com/clue/reactphp-flux/workflows/CI/badge.svg)](https://github.com/clue/reactphp-flux/actions)
 
 Flux, the lightweight stream processor to concurrently do many (but not too many) things at once,
 built on top of [ReactPHP](https://reactphp.org/).