Update lib/ancestry/has_ancestry.rb

Use stabby lambda for named scope in order to be compatible with rails 4 and use ruby 1.9 syntax
forgot some code in previous commit
Removed occurence of ::scoped() call which will be deprecated
Update has_ancestry.rb

used the lambda keyword instead of stabby lambda in order to keep compatibility with older versions
Merge branch 'master' of git://github.com/Systho/ancestry into Systho-master