Inherit the colors for correct and mistake faces from default faces

Since there is a huge variance in the visibility of green and red in
various themes it might be better to inherit the colors for
speed-type-correct and speed-type-mistake from the the success and
warning faces. The reason to not inherit from them directly was
in-case the theme does something weird like using a different weight
or having boxes etc...

speed-type.el

@@ -109,12 +109,12 @@ To remove without replacement, use the form: `(bad-string . \"\")'"
  :group 'speed-type)
 
 (defface speed-type-correct
- '((t :foreground "green"))
+ `((t (:inherit 'default :foreground ,(face-foreground 'success))))
  "Face for correctly typed characters."
  :group 'speed-type)
 
 (defface speed-type-mistake
- '((t :foreground "red" :underline "red"))
+ `((t (:inherit 'default :foreground ,(face-foreground 'error) :underline t)))
  "Face for incorrectly typed characters."
  :group 'speed-type)