Update query-builder.rst

expresion substr changed to substring as of
http://www.doctrine-project.org/jira/browse/DDC-382
Merge pull request #795 from sabzeta/patch-1

Update query-builder.rst
Second cache level POC
First round of refactory
Fix factory method name
refactoring region access tests
basically support for many to many collection
Refactoring tests
store cascade collections
refactoring collections store
handle one to many collections storage
tests put entities on persist
test one to many orphan removal
drop support for Region#toArray and Region#count
Configurable cache interface
test DefaultCache
drop cache key api from cache interface
refactoring default cache test
Basic interaction between query and second level cache
add cache entry and configurable region lifetime