minor jira change

[Paul King <pa...@asert.com.au>]

I just made a minor change of the 2.x version to 3.x.

Some background: In Jira, we use 2.4.x, 2.5.x etc. as meta versions for
loosely scheduling work - usually to indicate that a later version for a
particular change is anticipated/desired. We never leave that as the fix
version once an issue is resolved.

Given that we will probably target master (3+) for most new work, it
doesn't seem worthwhile having the 2.x version anymore (hence the change).
Most of the issues with that version are quite old in any case.

As a second pass, we can go through and see if any issues now under 3.x
could target 2.5.x. And similarly, we should see if any under 2.4.x should
be 2.5.x or 3.x.

Cheers, Paul.