Reword initial *scratch* for brevity, appearance

* lisp/startup.el (initial-scratch-message):
Reword to avoid apostrophes, and to make it shorter.
See the thread starting in:
http://lists.gnu.org/archive/html/emacs-devel/2015-12/msg01241.html

lisp/startup.el

@@ -1430,9 +1430,8 @@ settings will be marked as \"CHANGED outside of Customize\"."
      (put 'cursor 'face-modified t))))

(defcustom initial-scratch-message (purecopy "\
;; This buffer is for notes you don\\='t want to save, and for Lisp evaluation.
;; If you want to create a file, visit that file with \\[find-file],
;; then enter the text in that file\\='s own buffer.
;; This buffer is for text that is not saved, and for Lisp evaluation.
;; To create a file, visit it with \\[find-file] and enter text in its buffer.

")
  "Initial documentation displayed in *scratch* buffer at startup.