Replace Travis by Github Actions

Squashed commit of the following:

commit 56c1911
Author: Aron Rotteveel <[email protected]>
Date:   Thu Apr 30 11:25:09 2020 +0200

    Bye, Travis!

commit 02e3768
Author: Aron Rotteveel <[email protected]>
Date:   Thu Apr 30 11:23:29 2020 +0200

    Update Mockery to (hopefully) fix test issues

commit 086e587
Author: Aron Rotteveel <[email protected]>
Date:   Thu Apr 30 11:16:04 2020 +0200

    Do not test for Laravel 5.8

commit 2adf6e9
Author: Aron Rotteveel <[email protected]>
Date:   Thu Apr 30 11:11:16 2020 +0200

    Added Github actions workflow

.github/workflows/run-tests.yml

@@ -0,0 +1,45 @@
+name: "Run Tests"
+
+on: [push, pull_request]
+
+jobs:
+  test:
+
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: true
+      matrix:
+        php: [7.4, 7.3, 7.2]
+        laravel: [7.*, 6.*]
+        dependency-version: [prefer-lowest, prefer-stable]
+        include:
+          - laravel: 7.*
+            testbench: 5.*
+          - laravel: 6.*
+            testbench: 4.*
+
+    name: P${{ matrix.php }} - L${{ matrix.laravel }} - ${{ matrix.dependency-version }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v1
+
+      - name: Cache dependencies
+        uses: actions/cache@v1
+        with:
+          path: ~/.composer/cache/files
+          key: dependencies-laravel-${{ matrix.laravel }}-php-${{ matrix.php }}-composer-${{ hashFiles('composer.json') }}
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: curl, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, iconv
+          coverage: none
+
+      - name: Install dependencies
+        run: |
+          composer require "laravel/framework:${{ matrix.laravel }}" "orchestra/testbench:${{ matrix.testbench }}" "symfony/console:>=4.3.4" --no-interaction --no-update
+          composer update --${{ matrix.dependency-version }} --prefer-dist --no-interaction --no-suggest
+      - name: Execute tests
+        run: vendor/bin/phpunit

composer.json

@@ -21,12 +21,12 @@
     ],
     "require": {
         "php": "^7.2",
-        "illuminate/http": "^7.0"
+        "illuminate/http": "^6.0|^7.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^8.0",
-        "orchestra/testbench": "^5.1",
-        "mockery/mockery": "^1.0"
+        "orchestra/testbench": "^4.0|^5.0",
+        "mockery/mockery": "^1.3"
     },
     "autoload": {
         "psr-4": {