[Fix clojure-emacs#506] Provide (lm-version) with a buffer with content

the the content should be (at least) the headers up to Version, so
that (lm-version) can fetch it.

clojure-mode.el

@@ -10,7 +10,7 @@
 ;;       Artur Malabarba <[email protected]>
 ;; URL: http://github.com/clojure-emacs/clojure-mode
 ;; Keywords: languages clojure clojurescript lisp
-;; version: 5.10.0
+;; Version: 5.10.0
 ;; Package-Requires: ((emacs "25.1"))
 
 ;; This file is not part of GNU Emacs.
@@ -81,7 +81,10 @@
   :link '(url-link :tag "GitHub" "https://github.com/clojure-emacs/clojure-mode")
   :link '(emacs-commentary-link :tag "Commentary" "clojure-mode"))
 
-(defconst clojure-mode-version (lm-version)
+(defconst clojure-mode-version
+  (let ((thisbuffer (or load-file-name buffer-file-name)))
+    (with-temp-buffer (insert-file-contents thisbuffer)
+                      (lm-version)))
   "The current version of `clojure-mode'.")
 
 (defface clojure-keyword-face