Fix syn dependency in codegen crate
diff --git a/codegen/Cargo.toml b/codegen/Cargo.toml
index ed5029b..e50dc42 100644
--- a/codegen/Cargo.toml
+++ b/codegen/Cargo.toml
@@ -6,7 +6,7 @@
 publish = false # this is an internal crate which should never be published
 
 [dependencies]
-syn = { path = "..", features = ["full", "extra-traits"] }
+syn-next = { path = "..", features = ["full", "extra-traits"] }
 quote = "0.6"
 failure = "0.1"
 inflections = "1.1"