Directly depend on magit-popup

`magit' uses `transient' instead of `magit-popup' now.  Because
`magit-stgit' still uses `magit-popup' it has to depend on that
itself.

This makes it necessary to bump the `magit' dependency too.
`magit-popup' was split from `magit' in 2.12.0, so we have depend
on that version of both packages.

The dependency specification should be:

    ((emacs "24.4")
     (or ((magit "2.1.0 <= v < " 2.12.0"))
         ((magit "2.12.0")
          (magit-popup "2.12.0"))))

But `package.el' does not support that.

Author: tarsius

magit-stgit.el

@@ -1,12 +1,12 @@
 ;;; magit-stgit.el --- StGit extension for Magit
 
-;; Copyright (C) 2011-2017  The Magit Project Contributors
+;; Copyright (C) 2011-2019  The Magit Project Contributors
 
 ;; Author: Lluís Vilanova <[email protected]>
 ;; Maintainer: Lluís Vilanova <[email protected]>
 ;; Keywords: vc tools
 ;; Package: magit-stgit
-;; Package-Requires: ((emacs "24.4") (magit "2.1.0"))
+;; Package-Requires: ((emacs "24.4") (magit "2.12.0") (magit-popup "2.12.0")
 
 ;; Magit is free software; you can redistribute it and/or modify it
 ;; under the terms of the GNU General Public License as published by
@@ -58,6 +58,7 @@
 (require 'dash)
 
 (require 'magit)
+(require 'magit-popup)
 
 ;;; Options
 ;;;; Variables