ob-awk: safer variable expansion

* lisp/ob-awk.el (org-babel-expand-body:awk): Allow for symbolic
  variable names.

lisp/ob-awk.el

@@ -48,7 +48,7 @@
   "Expand BODY according to PARAMS, return the expanded body."
   (dolist (pair (mapcar #'cdr (org-babel-get-header params :var)))
     (setf body (replace-regexp-in-string
-                (regexp-quote (concat "$" (car pair))) (cdr pair) body)))
+                (regexp-quote (format "$%s" (car pair))) (cdr pair) body)))
   body)
 
 (defun org-babel-execute:awk (body params)