Revert PHPUnit config to work with PHPUnit 8

Author: iquito

phpunit.xml.dist

@@ -1,13 +1,20 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" backupGlobals="false" colors="true" bootstrap="vendor/autoload.php">
-  <coverage>
-    <include>
-      <directory suffix=".php">src</directory>
-    </include>
-  </coverage>
-  <testsuites>
-    <testsuite name="Unit Tests">
-      <directory>tests</directory>
-    </testsuite>
-  </testsuites>
-</phpunit>
+<phpunit
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/6.3/phpunit.xsd"
+         backupGlobals="false"
+         colors="true"
+         bootstrap="vendor/autoload.php"
+>
+    <testsuites>
+        <testsuite name="Unit Tests">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+
+    <filter>
+        <whitelist>
+            <directory suffix=".php">src</directory>
+        </whitelist>
+    </filter>
+</phpunit>