Add case for DB2 v13 -- Ruby connection is failing

[matthewkrom]

Can support for DB2 v13 be added here ASAP? There's no case here (in ibm_db_adapter.rb) for when /13/, and I believe 13 is the latest version. Our DB2 client started failing today. In the past, we've monkey-patched our versions when this happened...

when /DB2/i # DB2 for zOS
case server_info.DBMS_VER
when /09/ # DB2 for zOS version 9 and version 10
@servertype = IBM_DB2_ZOS.new(self, @isar3)
when /10/
@servertype = IBM_DB2_ZOS.new(self, @isar3)
when /11/
@servertype = IBM_DB2_ZOS.new(self, @isar3)
when /12/
@servertype = IBM_DB2_ZOS.new(self, @isar3)
when /08/ # DB2 for zOS version 8
@servertype = IBM_DB2_ZOS_8.new(self, @isar3)
else # DB2 for zOS version 7
raise 'Only DB2 z/OS version 8 and above are currently supported'
end

[praveen-db2]

@matthewkrom feel free to do changes, test it and create PR for the same.
I will approve the PR once I review.

[matthewkrom]

@praveen-db2 Please review #191 thank you!

[matthewkrom]

@praveen-db2 if you have a time estimate at any point, that could help. Right now me and a small team is working on monkey-patching the ibm_db gem, but it's causing side-effects and we don't have a production-ready monkey patch at the moment... if there were a new Gem version we could drop it in... Thank you.

[matthewkrom]

Update: Our patching has worked, for now. It is inelegant. We'll be watching for possible new version here that connects against DB2 v13. Sorry for the blow-by-blow, but it seems nobody else has been affected by DB2 v13 being rolled out so far(?)

[praveen-db2]

@matthewkrom I will try doing it next month. I need to address other issue as well #189.
Together I will release new gem version.