Work with existing composer file; but force a fresh install to require new dependency versions

.travis.yml

@@ -16,7 +16,6 @@ before_script:
   # Deactivate xdebug
   - if [[ $TRAVIS_PHP_VERSION != nightly ]]; then phpenv config-rm xdebug.ini; fi
   - if [[ $TRAVIS_PHP_VERSION == nightly ]]; then rm composer.lock; fi
-  - if [[ $TRAVIS_PHP_VERSION == nightly ]]; then cp composer.php8.json composer.json; fi
   - composer install --ignore-platform-reqs
 
 script:

composer.php8.json

@@ -1,89 +0,0 @@
-{
-  "name": "phpoffice/phpspreadsheet",
-  "description": "PHPSpreadsheet - Read, Create and Write Spreadsheet documents in PHP - Spreadsheet engine",
-  "keywords": ["PHP", "OpenXML", "Excel", "xlsx", "xls", "ods", "gnumeric", "spreadsheet"],
-  "homepage": "https://github.com/PHPOffice/PhpSpreadsheet",
-  "type": "library",
-  "license": "MIT",
-  "authors": [
-    {
-      "name": "Maarten Balliauw",
-      "homepage": "https://blog.maartenballiauw.be"
-    },
-    {
-      "name": "Mark Baker",
-      "homepage": "https://markbakeruk.net"
-    },
-    {
-      "name": "Franck Lefevre",
-      "homepage": "https://rootslabs.net"
-    },
-    {
-      "name": "Erik Tilt"
-    },
-    {
-      "name": "Adrien Crivelli"
-    }
-  ],
-  "scripts": {
-    "check": [
-      "php-cs-fixer fix --ansi --dry-run --diff",
-      "phpcs",
-      "phpunit --color=always"
-    ],
-    "fix": [
-      "php-cs-fixer fix --ansi"
-    ],
-    "versions": [
-      "phpcs --report-width=200 samples/ src/ tests/ --ignore=samples/Header.php --standard=PHPCompatibility --runtime-set testVersion 7.2- -n"
-    ]
-  },
-  "require": {
-    "php": "^7.2|^8.0",
-    "ext-ctype": "*",
-    "ext-dom": "*",
-    "ext-gd": "*",
-    "ext-iconv": "*",
-    "ext-fileinfo": "*",
-    "ext-libxml": "*",
-    "ext-mbstring": "*",
-    "ext-SimpleXML": "*",
-    "ext-xml": "*",
-    "ext-xmlreader": "*",
-    "ext-xmlwriter": "*",
-    "ext-zip": "*",
-    "ext-zlib": "*",
-    "maennchen/zipstream-php": "^2.1",
-    "markbaker/complex": "^1.5|^2.0",
-    "markbaker/matrix": "^1.2|^2.0",
-    "psr/simple-cache": "^1.0",
-    "psr/http-client": "^1.0",
-    "psr/http-factory": "^1.0"
-  },
-  "require-dev": {
-    "dompdf/dompdf": "^0.8.5",
-    "friendsofphp/php-cs-fixer": "^2.16",
-    "jpgraph/jpgraph": "^4.0",
-    "mpdf/mpdf": "^8.0",
-    "phpcompatibility/php-compatibility": "^9.3",
-    "phpunit/phpunit": "^9.3",
-    "squizlabs/php_codesniffer": "^3.5",
-    "tecnickcom/tcpdf": "^6.3"
-  },
-  "suggest": {
-    "mpdf/mpdf": "Option for rendering PDF with PDF Writer",
-    "dompdf/dompdf": "Option for rendering PDF with PDF Writer",
-    "tecnickcom/tcpdf": "Option for rendering PDF with PDF Writer",
-    "jpgraph/jpgraph": "Option for rendering charts, or including charts with PDF or HTML Writers"
-  },
-  "autoload": {
-    "psr-4": {
-      "PhpOffice\\PhpSpreadsheet\\": "src/PhpSpreadsheet"
-    }
-  },
-  "autoload-dev": {
-    "psr-4": {
-      "PhpOffice\\PhpSpreadsheetTests\\": "tests/PhpSpreadsheetTests"
-    }
-  }
-}