Perhaps we should do something smarter here.
Instead of having to keep updating this file when master branch changes or a branch is removed. We could have a script that given a `MAJOR.MINOR` version it would try to figure out what is the best `ref` for it.

I've created a small script that does this:
```
./latest_ref.sh 2.0 // outputs 2.0.6
./latest_ref.sh 2.1 // outputs 2.1.5
./latest_ref.sh 2.2 // outputs 2.2.9
./latest_ref.sh 2.3 // outputs 2.3.10
./latest_ref.sh 2.4 // outputs master
./latest_ref.sh 2.5 // outputs 2.5
```

As you notice, the last two matches a branch.

I will finish up my script and change the repositories if you think this is a good idea.