Filter on oracle driver

**Describe the bug**
when using playground react app, with oracle 18c DB, i got errors on request ' Illegal variable name/number'

**To Reproduce**
install the cubejs playground with oracle DB

**Expected behavior**
return request

**Additional info**
1- when using filter "contains", i've got || ? || unstead of || :"?" ||
2- the alias generated it got used ` caracter that also generated errors
3- the connection is not closed when an error is thrown

to avoid these issues , i did a workround on updating the query variable on oracle driver and closing correctly with finally and release