Update dependency cimg/php to v8.1

Author: renovate-bot

.circleci/config.yml

@@ -6,7 +6,7 @@ version: 2
 jobs:
   php71:
     docker:
-      - image: cimg/php:7.1
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: sudo apt update -y
@@ -16,7 +16,7 @@ jobs:
       - run: XDEBUG_MODE=coverage php vendor/bin/phpunit --coverage-text
   php72:
     docker:
-      - image: cimg/php:7.2
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: sudo apt update -y
@@ -26,7 +26,7 @@ jobs:
       - run: XDEBUG_MODE=coverage php vendor/bin/phpunit --coverage-text
   php73:
     docker:
-      - image: cimg/php:7.3
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: sudo apt update -y
@@ -36,7 +36,7 @@ jobs:
       - run: XDEBUG_MODE=coverage php vendor/bin/phpunit --coverage-text
   php74:
     docker:
-      - image: cimg/php:7.4
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: sudo apt update -y
@@ -46,7 +46,7 @@ jobs:
       - run: XDEBUG_MODE=coverage php vendor/bin/phpunit --coverage-text
   php80:
     docker:
-      - image: cimg/php:8.0
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: php -v