Invalid default value for calculator setting (unit test failure)

[micaherne]

The default value for the mod_peerwork\calculator setting - zero - is not valid and causes the Moodle core unit test core\adminlib_test::test_admin_apply_default_settings to fail.

2) core\adminlib_test::test_admin_apply_default_settings
Failed asserting that two arrays are identical.
--- Expected
+++ Actual
@@ @@
-Array &0 ()
+Array &0 (
+    'peerwork/calculator' => '0'
+)

/var/www/html/lib/tests/adminlib_test.php:173
/var/www/html/lib/phpunit/classes/advanced_testcase.php:81

[amandadoughty]

Fix merged