avoid error in Read instance and use pfail instead which causes nicer…

… and more useful option error message to be shown

src/Types/Commands.hs

@@ -53,7 +53,7 @@ instance Read BuildType where
     case map toLower s of
         "carthage"   -> return Carthage
         "podbuilder" -> return PodBuilder
-        a            -> error $ "Unrecognized BuildType '" ++ a ++ "'"
+        _ -> pfail
 
 data RomeListPayload = RomeListPayload { _listMode              :: ListMode
                                        , _listPlatforms         :: [TargetPlatform]