Fix typo in org-bibtex.el comments

lisp/org-bibtex.el

@@ -27,7 +27,7 @@
 ;; This file implements links to database entries in BibTeX files.
 ;; Instead of defining a special link prefix, it uses the normal file
 ;; links combined with a custom search mechanism to find entries
-;; by reference key.  And it constucts a nice description tag for
+;; by reference key.  And it constructs a nice description tag for
 ;; the link that contains the author name, the year and a short title.
 ;;
 ;; It also stores detailed information about the entry so that