Release.colorized(), not std::fmt::Display

I don't know for sure if the string-ified version of a Release struct is
being printed to the terminal. As such, I don't know if the user wants,
does not want, or has mixed intentions for the stringification of this
thing.

No Display impl, instead just a `colorized()` method.

src/main.rs

@@ -40,7 +40,7 @@ async fn main() -> Result<(), gt_tool::Error> {
                 releases
                     .iter()
                     .rev()
-                    .map(|release| release.to_string()),
+                    .map(|release| release.colorized()),
                     String::from("")
                 )
                 .map(|release| println!("{}", release))