[test] Address `warning: Ambiguous first argument; make sure.` (#848)
[test] Address `warning: Ambiguous first argument; make sure.` (#848)

```ruby
$ rake test_mysql
Using ActiveRecord::VERSION = 5.1.4
/home/yahonda/git/activerecord-jdbc-adapter/test/db/mysql/simple_test.rb:191:
warning: Ambiguous first argument; make sure.
```
kares/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter