fix(kernel/formatter): add missing parentheses

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/kernel/formatter.cpp

@@ -164,7 +164,10 @@ struct print_expr_fn {
             bool first = true;
             for (auto l : ls) {
                 if (first) first = false; else out() << " ";
-                out() << l;
+                if (is_max(l) || is_imax(l))
+                    out() << "(" << l << ")";
+                else
+                    out() << l;
             }
             out() << "}";
         }