[tlbuild] [tex-live] laulatex quiting: fix your writable cachepath

[Élie Roux]

> Fact remains that I am still not certain whether the problem is a source bug or a build bug.

I planned once to build the binary from the TL SVN, but it seems complex 
to build only the LuaTeX binary and not all (which would take too much 
time on my old laptop), is there a way to select only one ?

Thank you,
-- 
Elie