fix compile error with new syn version

Author: NyxCode

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "proxy-enum"
-version = "0.3.0"
+version = "0.3.1"
 authors = ["Moritz Bischof <[email protected]>"]
 edition = "2018"
 description = "Emulate dynamic dispatch and sealed classes using a proxy enum, which defers all method calls to its variants."

src/lib.rs

@@ -135,7 +135,7 @@ extern crate proc_macro2;
 use proc_macro::TokenStream;
 use std::collections::HashMap;
 
-use syn::export::TokenStream2;
+use proc_macro2::TokenStream as TokenStream2;
 use syn::visit_mut::VisitMut;
 use syn::{
     parse2, parse_macro_input, Attribute, Fields, FnArg, Ident, ImplItem, Item, ItemEnum, ItemImpl,