Add "radical" as an alias for "redical" theme

The "redical" theme appears to have been introduced as a misspelling of
"radical" (its color palette matches the radical theme of
anuraghazra/github-readme-stats exactly). A previous rename attempt
(#236) was closed to avoid breaking users who already configured
theme=redical.

This change keeps "redical" working as before and adds "radical" as a
fall-through alias with the same colors, so newcomers can discover the
canonical name without disrupting existing users.