delete trailing whitespace in phpunit.xml

phpunit.xml

@@ -12,7 +12,7 @@
         <testsuite name="Unit">
             <directory suffix="Test.php">./tests/Unit</directory>
         </testsuite>
-        
+
         <testsuite name="Feature">
             <directory suffix="Test.php">./tests/Feature</directory>
         </testsuite>