Fix test failures

https://travis-ci.org/yiisoft/yii2/jobs/38423752#L869

```
There were 2 failures:

1) yiiunit\framework\db\cubrid\CubridQueryBuilderTest::testSelectSubquery
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'SELECT *, (SELECT COUNT(*) FROM `operations` WHERE account_id = accounts.id) AS `operations_count` FROM `accounts`'
+'SELECT *, (SELECT COUNT(*) FROM "operations" WHERE account_id = accounts.id) AS "operations_count" FROM "accounts"'

/home/travis/build/yiisoft/yii2/tests/unit/framework/db/QueryBuilderTest.php:438
/home/travis/build/yiisoft/yii2/vendor/phpunit/phpunit/composer/bin/phpunit:63

2) yiiunit\framework\db\pgsql\PostgreSQLQueryBuilderTest::testSelectSubquery
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'SELECT *, (SELECT COUNT(*) FROM `operations` WHERE account_id = accounts.id) AS `operations_count` FROM `accounts`'
+'SELECT *, (SELECT COUNT(*) FROM "operations" WHERE account_id = accounts.id) AS "operations_count" FROM "accounts"'

/home/travis/build/yiisoft/yii2/tests/unit/framework/db/QueryBuilderTest.php:438
/home/travis/build/yiisoft/yii2/vendor/phpunit/phpunit/composer/bin/phpunit:63
```