Switch to LGPL (prettyerr)

diff --git a/ast b/ast
index 24a5f882a8c2e6ebddf8e05f19a8de0a94d884e1..a75405923327ccb7636190044e2b994b26c2a3e7 160000 (submodule)
--- a/ast
+++ b/ast
@@ -1 +1 @@
-Subproject commit 24a5f882a8c2e6ebddf8e05f19a8de0a94d884e1
+Subproject commit a75405923327ccb7636190044e2b994b26c2a3e7