Add syn to graphql_client_cli

Author: h-michael

graphql_client_cli/Cargo.toml

@@ -18,6 +18,7 @@ structopt = "0.2"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
+syn = "0.15"
 
 rustfmt-nightly = { version = "0.99" , optional = true }