feat(theme): change default ansi color theme

Change the default ansi color theme to use colors that are more similar
to the colors from the default RGB theme. In particular, don't use red
for any of the span labels, since that color is also used for errors.

src/handlers/theme.rs

@@ -125,9 +125,9 @@ impl ThemeStyles {
             link: style().cyan().underline().bold(),
             linum: style().dimmed(),
             highlights: vec![
-                style().red().bold(),
+                style().magenta().bold(),
                 style().yellow().bold(),
-                style().cyan().bold(),
+                style().green().bold(),
             ],
         }
     }