Remove debug print to stdout in trade sub command (#191)

Every time when the `trade` sub command is executed, the webpage gets
printed to stdout which is a bit irritating and unnecessary.

This PR fixes this, in that it changes the `println!` macro to a
`trace!` macro.

steamguard/src/lib.rs

@@ -163,7 +163,7 @@ impl SteamGuardAccount {
 		trace!("{:?}", resp);
 		let text = resp.text().unwrap();
 		trace!("text: {:?}", text);
-		println!("{}", text);
+		trace!("{}", text);
 		return parse_confirmations(text);
 	}