Specify that the greatest version we can support of the activerecord-jdbc-adapter is 1.2.9.1

I had been doing some work and testing with a clean install of JRuby, and when I did a 'bundle install' that included the latest version of the activerecord-jdbcteradata-adapter (0.5.1), I was finding that even basic INSERT and SELECT operations were not working properly.

I found that the root cause of this issue was that the gemspec for activerecord-jdbcteradata-adapter 0.5.1 adds a dependency on 'activerecord-jdbc-adapter', but does not specify a specific version number for that dependency, so by default, the most recent version is fetched.

It seems there have been some major (breaking) changes in the 1.3.x line of 'activerecord-jdbc-adapter', for which the specs for this AR JDBC Teradata adapter no longer pass..  While it probably makes sense at some point to dig through and make this AR JDBC Teradata adapter compatible with the 1.3.x line of the AR JDBC Adapter, for right now, a quick fix is to just specify that the latest version of the AR JDBC Adapter that is supported is 1.2.9.1.   With this in place, the specs all pass.