gnu: emacs-ghub: Update to 3.2.0.

* gnu/packages/emacs-xyz.scm (emacs-ghub): Update to 3.2.0.
[propagated-inputs]: Add emacs-dash, emacs-graphql, emacs-treepy.
[synopsis, description]: Update.
(emacs-magit, emacs-magit-svn)[propagated-inputs]: Add emacs-graphql,
emacs-treepy.
[arguments]: Update accordingly.