outcome printer: `test/class.t` tests show failure

[anmonteiro]

there's a bug in outcome printing of class types, e.g.

class labeledClass2(~x: ((~y:int) => int)) {
};

$ echo "class labeledClass2(~x: ((~y:int) => int)) {
};
" | dune exec test/lib/outcometreePrinter.exe
class labeledClass2 : (~x: int, int) => {  };