Support PHP 8.1 (#43)

Author: GrahamCampbell

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Install dependencies
-        run: composer update --no-interaction --prefer-stable --prefer-lowest --no-progress --prefer-dist
+        run: composer update --no-interaction --prefer-stable --prefer-lowest --no-progress
 
       - name: Run tests
         run: make test
@@ -34,7 +34,7 @@ jobs:
     strategy:
       max-parallel: 10
       matrix:
-        php: ['7.2', '7.3', '7.4', '8.0']
+        php: ['7.2', '7.3', '7.4', '8.0', '8.1']
 
     steps:
       - name: Set up PHP
@@ -47,8 +47,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v2
 
+      - name: Mimic PHP 8.0
+        run: composer config platform.php 8.0.999
+        if: matrix.php > 8
+
       - name: Install dependencies
-        run: composer update --no-interaction --no-progress --prefer-dist
+        run: composer update --no-interaction --no-progress
 
       - name: Run tests
         run: make test