Update tutorial-using-oracle.md

1. schema name www.Liquibase.org does not work, changed it to www.liquibase.org in the whole document.
2. Diff command syntax has changed, updated it to following

Liquibase diff --referenceUrl=jdbc:oracle:thin:@localhost:1521:XE --referenceUsername=lb_test --referencePassword=lb_test
Revert "Update tutorial-using-oracle.md"

This reverts commit fbd30f422ee652a76fead0bf290c245da4868f62.
XML schema name www.Liquibase.org has changed to www.liquibase.org.
Existing examples don't work unless changed to www.liquibase.org.
Diff command syntax has changed and the command no longer works. Changed the command.
Merge pull request #50 from ursdino/master

Changes to Oracle tutorial