Update default.rb

Error using last download_base i suggest to use for example http://astro-wise.org/instantclient

Errno::ETIMEDOUT
----------------
Error connecting to http://exodus.socsci.umn.edu/redhat/oracle-instantclient/instantclient-basic-linux.x64-11.2.0.3.0.zip - Connection timed out - connect(2)
Merge pull request #2 from mordonez/patch-1

Update default.rb