Use master database in sp_add_jobstep call

[DanielLoth]

Dave Dustin's issue - #7 - identified an issue with the use of sp_add_jobstep on a non-master database.

This change resolves that by:

• Specifying master for the @database_name parameter
• Using a use <database_name> statement in the SQL query that is the job step.

Thanks to Dave for pointing this one out.

[DanielLoth]

Closes #7