Upgrade to PHPUnit 7/8

Author: JaZo

.gitignore

@@ -3,6 +3,7 @@ composer.phar
 composer.lock
 /vendor/
 /.php_cs.cache
+/.phpunit.result.cache
 /node_modules/
 /docs/.vuepress/dist/
 /docs/README.md

composer.json

@@ -31,7 +31,7 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.14",
         "php-http/guzzle6-adapter": "^2.0",
-        "phpunit/phpunit": "^6.0"
+        "phpunit/phpunit": "^7.0|^8.0"
     },
     "provide": {
         "php-http/async-client-implementation": "1.0",

phpunit.xml.dist

@@ -8,7 +8,6 @@
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          bootstrap="./vendor/autoload.php"
 >
     <testsuites>

tests/ClientTest.php

@@ -17,7 +17,7 @@ class ClientTest extends TestCase
     public function it_can_send_a_request()
     {
         $request = new Request('GET', new Uri('http://example.com'));
-        /** @var \PHPUnit_Framework_MockObject_MockObject|\Swis\Http\Fixture\ResponseBuilderInterface $responseBuilder */
+        /** @var \PHPUnit\Framework\MockObject\MockObject&\Swis\Http\Fixture\ResponseBuilderInterface $responseBuilder */
         $responseBuilder = $this->getMockBuilder(ResponseBuilderInterface::class)->getMock();
         $responseBuilder->expects($this->once())
             ->method('build')