Update phpunit/phpunit requirement from ^6.0 || ^7.0 to ^7.0 || ^8.0 (#12)

* Update phpunit/phpunit requirement from ^6.0 || ^7.0 to ^6.0 || ^7.0 || ^8.0

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-8.1.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/commits/8.1.3)

Signed-off-by: dependabot[bot] <support@dependabot.com>

* Update composer.json

* Update README.md

* Update .travis.yml

Author: dependabot[bot]

.travis.yml

@@ -39,4 +39,5 @@ cache:
 branches:
   except:
   - /.*\-dev$/
-  
+  - /.*\-patch(\-\d+)?$/
+  

README.md

@@ -1,5 +1,6 @@
 # Symfony JSON-RPC Http server OpenAPI documentation
-[![License](https://img.shields.io/github/license/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg)](https://github.com/yoanm/symfony-jsonrpc-http-server-openapi-doc) [![Code size](https://img.shields.io/github/languages/code-size/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg)](https://github.com/yoanm/symfony-jsonrpc-http-server-openapi-doc) [![Dependencies](https://img.shields.io/librariesio/github/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg)](https://libraries.io/packagist/yoanm%2Fsymfony-jsonrpc-http-server-openapi-doc)
+[![License](https://img.shields.io/github/license/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg)](https://github.com/yoanm/symfony-jsonrpc-http-server-openapi-doc) [![Code size](https://img.shields.io/github/languages/code-size/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg)](https://github.com/yoanm/symfony-jsonrpc-http-server-openapi-doc) [![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=yoanm/symfony-jsonrpc-http-server-openapi-doc)](https://dependabot.com)
+
 
 [![Scrutinizer Build Status](https://img.shields.io/scrutinizer/build/g/yoanm/symfony-jsonrpc-http-server-openapi-doc.svg?label=Scrutinizer&logo=scrutinizer)](https://scrutinizer-ci.com/g/yoanm/symfony-jsonrpc-http-server-openapi-doc/build-status/master) [![Scrutinizer Code Quality](https://img.shields.io/scrutinizer/g/yoanm/symfony-jsonrpc-http-server-openapi-doc/master.svg?logo=scrutinizer)](https://scrutinizer-ci.com/g/yoanm/symfony-jsonrpc-http-server-openapi-doc/?branch=master) [![Code Coverage](https://img.shields.io/scrutinizer/coverage/g/yoanm/symfony-jsonrpc-http-server-openapi-doc/master.svg?logo=scrutinizer)](https://scrutinizer-ci.com/g/yoanm/symfony-jsonrpc-http-server-openapi-doc/?branch=master)
 

composer.json

@@ -39,7 +39,7 @@
   "require-dev": {
     "behat/behat": "~3.0",
     "squizlabs/php_codesniffer": "3.*",
-    "phpunit/phpunit": "^6.0 || ^7.0",
+    "phpunit/phpunit": "^7.0 || ^8.0",
     "matthiasnoback/symfony-dependency-injection-test": "^2.0 || ^3.0",
     "matthiasnoback/symfony-config-test": "^3.0 || ^4.0",
     "symfony/framework-bundle": "^3.0 || ^4.0",