cli: make hints cyan instead of blue

It's hard to read dark blue on black, at least with iTerm2's default
color scheme. Cyan makes it much more readable. That's the color
`cargo` uses. We could also consider coloring only the "Hint:" part
like `cargo` does. For errors, `cargo` colors the "Error:" part red
and uses bold/bright white for select parts of the message.

src/config/colors.toml

@@ -1,7 +1,7 @@
 [colors]
 "error" = "red"
 "warning" = "yellow"
-"hint" = "blue"
+"hint" = "cyan"
 
 "conflict_description" = "yellow"
 "conflict_description difficult" = "red"