Add `gem 'ruby-oci8'` explicitly for CRuby users
Add `gem 'ruby-oci8'` explicitly for CRuby users

rsim/oracle-enhanced,cdinger/oracle-enhanced,yahonda/oracle-enhanced,cdinger/oracle-enhanced,luke2237/oracle-enhanced,luke2237/oracle-enhanced,ifad/oracle-enhanced,ifad/oracle-enhanced,rshell/oracle-enhanced,rsim/oracle-enhanced,rshell/oracle-enhanced,ifad/oracle-enhanced,yahonda/oracle-enhanced