Upgrade to phpunit 9

Author: zorac

.gitignore

@@ -5,4 +5,5 @@ vendor/
 build/
 test.php
 .project
-clover.xml
+clover.xml
+.phpunit.result.cache

.travis.yml

@@ -11,11 +11,10 @@ env:
 matrix:
     fast_finish: true
     include:
-        # - php: 5.5 is over EOL. phpunit does not support it anymore so we just ignore this version
-        - php: 5.6
-        - php: 7.0
-        - php: 7.1
-        - php: 7.2
+        # - php: <7.3 is over EOL. phpunit does not support it anymore so we just ignore this version
+        - php: 7.3
+        - php: 7.4
+        - php: 8.0
 
 before_install:
     # setup code climate reporter https://docs.codeclimate.com/docs/configuring-test-coverage

composer.json

@@ -30,7 +30,8 @@
         "guzzlehttp/guzzle": "^6.0|^7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8.0"
+        "phpunit/phpunit": "^9.5",
+        "dms/phpunit-arraysubset-asserts": "^0.2.1"
     },
     "autoload": {
         "psr-4": {