Update phpunit/phpunit requirement from ^6.0 || ^7.0 to ^7.0 || ^8.0 (#22)

* 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

@@ -39,3 +39,4 @@ cache:
 branches:
   except:
   - /.*\-dev$/
+  - /.*\-patch(\-\d+)?$/

README.md

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

composer.json

@@ -37,7 +37,7 @@
     "require-dev": {
         "behat/behat": "~3.0",
         "squizlabs/php_codesniffer": "3.*",
-        "phpunit/phpunit": "^6.0 || ^7.0",
+        "phpunit/phpunit": "^7.0 || ^8.0",
         "yoanm/php-unit-extended": "^1.0"
     }
 }