revert phpunit.xml to phpunit 7.4 compatibility

Author: Andy Vaughn

phpunit.xml.dist

@@ -1,12 +1,10 @@
-<phpunit bootstrap="_bootstrap.php">
-    <testsuites>
-        <testsuite name="All Tests">
-            <directory>tests</directory>
-        </testsuite>
-    </testsuites>
-    <coverage processUncoveredFiles="true">
-        <include>
+<phpunit bootstrap="_bootstrap.php" backupGlobals="false" processIsolation="false">
+    <testsuite name="AllTests">
+        <directory>tests</directory>
+    </testsuite>
+    <filter>
+        <whitelist processUncoveredFilesFromWhitelist="true">
             <directory suffix=".php">src</directory>
-        </include>
-    </coverage>
-</phpunit>
+        </whitelist>
+    </filter>
+</phpunit>