Update syn to 0.15

The update was fairly smooth. Note that this commit only updated the
syn version and fixed all errors. So in case the new syn version
introduced new features we could use -- this commit doesn't use
those.

Author: LukasKalbertodt

Cargo.toml

@@ -30,7 +30,7 @@ nightly = ["proc-macro2/nightly"]
 [dependencies]
 proc-macro2 = { version = "0.4.6" }
 quote = "0.6.3"
-syn = { version = "0.14.4", features = ["full", "visit-mut"] }
+syn = { version = "0.15", features = ["full", "visit", "visit-mut"] }
 
 [dev-dependencies]
 build-plan = "0.1.1"

src/analyze.rs

@@ -3,7 +3,6 @@ use std::collections::HashSet;
 use proc_macro2::Span as Span2;
 use syn::{
     Ident, ItemTrait, Lifetime, Block,
-    token::Apostrophe,
     visit::{Visit, visit_item_trait},
 };
 
@@ -89,7 +88,7 @@ crate fn find_suitable_param_names(trait_def: &ItemTrait) -> (Ident, Lifetime) {
         .find(|i| !visitor.lt_names.contains(i))
         .unwrap_or_else(|| Ident::new(PROXY_LT_PARAM_NAME, param_span()));
     let lt = Lifetime {
-        apostrophe: Apostrophe::new(param_span()),
+        apostrophe: param_span(),
         ident: lt_name,
     };