Fixed no-std error

Author: LucaCappelletti94

src/ast/ddl.rs

@@ -19,7 +19,13 @@
 //! (commonly referred to as Data Definition Language, or DDL)
 
 #[cfg(not(feature = "std"))]
-use alloc::{boxed::Box, format, string::String, vec, vec::Vec};
+use alloc::{
+    boxed::Box,
+    format,
+    string::{String, ToString},
+    vec,
+    vec::Vec,
+};
 use core::fmt::{self, Display, Write};
 
 #[cfg(feature = "serde")]