Add 1.13

[raw berry]

1.13 is sometimes better for multi-version servers as it gives access to fast swimming (not in 1.12 ofc) and most simple parkour jumps with walls are far easier on 1.13 than on 1.14 due to the changes on collision with how X and Z walls are calculated, making Z walls collision box slightly bigger (the same size as an X wall).

[pine roost]

There is no big reason to use 1.13 nowadays anymore

It costs money for lunar to maintain and update their client

And by adding 1.13 Lunar would have to spend more money in maintaining a version played by too little players