Bump strum_ crates to 0.16

This removes the transitive dependency of syn <1.0 and associated
crates entirely, bringing down dependency count and allowing to
use syn ^1.0 exclusively in upstream crates such as the Rust compiler
tree.

Author: Xanewok

Cargo.toml

@@ -26,8 +26,8 @@ rust-stemmers = { version = "1", optional = true }
 serde = "1"
 serde_derive = "1.0.34" # First verstion to support #[serde(flatten)]
 serde_json = "1"
-strum = "0.15"
-strum_macros = "0.15"
+strum = "0.16"
+strum_macros = "0.16"
 jieba-rs = "0.4.10"
 
 [features]