try_prompt_pkg_add: highlight 2nd env on "other" (JuliaLang#3429)

(cherry picked from commit e13a2ea)

src/REPLMode/REPLMode.jl

@@ -746,10 +746,11 @@ function try_prompt_pkg_add(pkgs::Vector{Symbol})
             push!(shown_envs, expanded_env)
         end
         menu = TerminalMenus.RadioMenu(option_list, keybindings=keybindings, pagesize=length(option_list))
+        default = min(2, length(option_list))
         print(ctx.io, "\e[1A\e[1G\e[0J") # go up one line, to the start, and clear it
         printstyled(ctx.io, " └ "; color=:green)
         choice = try
-            TerminalMenus.request("Select environment:", menu)
+            TerminalMenus.request("Select environment:", menu, cursor=default)
         catch err
             if err isa InterruptException # if ^C is entered
                 println(ctx.io)