Sort completion list

#### Legacy mode:

  ```console
  $ irb --legacy
  irb(main):001:0> l[TAB][TAB]
  lambda           load             local_variables  loop
  ```

#### Before this patch:

  ```console
  $ irb
  irb(main):001:0> l[TAB][TAB]
  local_variables
  loop
  lambda
  load
  ```

#### After this patch:

  ```console
  $ irb
  irb(main):001:0> l[TAB][TAB]
  lambda
  load
  local_variables
  loop
  ```

lib/reline/line_editor.rb

@@ -317,7 +317,7 @@ def rerender
     if @menu_info
       scroll_down(@highest_in_all - @first_line_started_from)
       @rerender_all = true
-      @menu_info.list.each do |item|
+      @menu_info.list.sort!.each do |item|
         Reline::IOGate.move_cursor_column(0)
         @output.print item
         @output.flush