Fix missing std-lib in a test

src/color.rs

@@ -109,6 +109,7 @@ mod tests {
     #[test]
     fn from_u8_panic() {
         for val in 2..=u8::max_value() {
+            extern crate std;
             let result = std::panic::catch_unwind(|| Color::from(val));
             assert!(result.is_err());
         }