Update composer.json, PHPUnit should be at latest version 7 version.

a7d9f85f · Chris Shantz · 63522c6e · a7d9f85f
Commit a7d9f85f authored Jan 27, 2020 by Chris Shantz
--- a/composer.json
+++ b/composer.json
@@ -103,7 +103,7 @@
        "mikey179/vfsstream": "v1.6.7",
        "onelogin/php-saml": "3.2.1",
        "oomphinc/composer-installers-extender": "v1.1.2",
-        "phpunit/phpunit": "6.5",
+        "phpunit/phpunit": "^7",
        "symfony/browser-kit": ">=2.8.13 <3.0",
        "symfony/css-selector": "~3.0",
        "symfony/finder": "^4.0",