fix an issue when we use alias in bazaar 

In berksfile if we use alias, when it's modified the berks update remains on the previous location.
This change fixes this issue
Update bzr.rb

remove wrong cut/paste
Update bzr.rb

fix issue for test
Update bzr_spec.rb

fix spec test
fix issue
Merge pull request #2 from gouketsu/patch-1

fix an issue when we use alias in bazaar