Update CI to test php 8.0 & 8.1

.travis.yml

@@ -19,17 +19,24 @@ jobs:
    - php: 7.2
    - php: 7.3
    - php: 7.4
-   - php: nightly
-     install: travis_retry composer config platform.php 7.4.0 && composer install
+   - php: 8.0
+   - php: 8.0
+     before_install:
+       - sudo apt-get -y install libonig-dev libzip-dev
+       - git clone git://github.com/php-build/php-build.git /home/travis/.phpenv/plugins/php-build
+       - sed -i 's/install_package_from_github master/install_package_from_github PHP-8.1/g' /home/travis/.phpenv/plugins/php-build/share/php-build/definitions/8.1snapshot
+       - phpenv install 8.1snapshot
+       - phpenv global 8.1snapshot
+       - php --version
+       - ln -s /home/travis/.phpenv/versions/8.0/bin/composer /home/travis/.phpenv/versions/8.1snapshot/bin/composer
   fast_finish: true
-  allow_failures:
-   - php: nightly # PHP 8 is still in beta
 
 services:
   - memcached
   - mysql
 
 before_script:
+  - sudo apt-get -y install ca-certificates openssl libssl-dev libssl1.0.0 libcurl3 libgnutls-openssl27 || return 0
   - mysql -e "create database IF NOT EXISTS test;" -uroot
 
 before_install: