Store span of function argument colon tokens
diff --git a/syntax/mod.rs b/syntax/mod.rs
index 3d56293..b2c524b 100644
--- a/syntax/mod.rs
+++ b/syntax/mod.rs
@@ -174,6 +174,7 @@
     pub attrs: OtherAttrs,
     pub visibility: Token![pub],
     pub name: Pair,
+    pub colon_token: Token![:],
     pub ty: Type,
 }