ob-lisp: Strip quotes from result value

* lisp/ob-lisp.el (org-babel-execute:lisp): Make sure that when
a singular string value is returned, it has no quotation marks around
it.

Before this change, the code below would produce an incorrect result:

  #+BEGIN_SRC lisp :results file
  "plot.png"
  #+END_SRC

  #+RESULTS:
  [[file:"plot.png"]]

After the change:

  #+BEGIN_SRC lisp :results file
  "plot.png"
  #+END_SRC

  #+RESULTS:
  [[file:plot.png]]

TINYCHANGE

lisp/ob-lisp.el

@@ -107,7 +107,7 @@ a property list containing the parameters of the block."
                                      (point-min) (point-max)))))
                               (cdr (assq :package params)))))))
      (org-babel-result-cond (cdr (assq :result-params params))
-       result
+       (org-strip-quotes result)
        (condition-case nil
            (read (org-babel-lisp-vector-to-list result))
          (error result))))