Improve description for dub search discovery

Removes "for D" as per dub recommendation that all packages on dub are for D and explicitly stating this is discouraged unless it's a port of another language's library.

Adds ok and err to the description to be more discoverable in search.

Author: WebFreak001

dub.sdl

@@ -1,5 +1,5 @@
 name "expected"
-description "Implementation of expected idiom for D"
+description "Implementation of expected idiom (error handling with ok and err)"
 authors "Tomáš Chaloupka"
 copyright "Copyright © 2019, Tomáš Chaloupka"
 license "BSL-1.0"