Tracker (+miners) 2.1.x is the stable series for GNOME 3.30

[Carlos Garnacho <carlosg gnome org>]

Hi!,

Probably my blog about Tracker 2 and its versioning scheme this went
largely missed/forgotten, hence I think it makes sense for this heads
up:

  Latest Tracker stable series is 2.1.x

As per https://blogs.gnome.org/carlosg/2017/06/11/next-tracker-is-2-0-0/,
Tracker adopted semantic versioning since 2.0. The new 2.1 series
means new API was added, but the new series preserve complete API and
ABI backwards compatibility with 2.0.x.

The new semantics have been mostly invisible till now, but I think
they're worth pointing out now since one of the implications of semver
is that even/odd numbers don't convey stability. These new 2.1.x
series are meant to be the stable series for 3.30.

I might send more reminders in the future whenever it might get
confusing, but changes like this within the cycle apply anytime in the
future too. How semver and gnome cycles will be made to fit neatly is
TBD, but rest assured there will be a 2.x series in time for freezes
and stabilized with it. 2.1.x will be it for 3.30.

Cheers,
  Carlos