Fixup parens in gnuplot-trim-gnuplot-buffer

Author: mtreca

gnuplot.el

@@ -1357,7 +1357,7 @@ This keeps that buffer from growing excessively in size.  Normally,
 this function is attached to `gnuplot-after-plot-hook'"
   (if (> gnuplot-buffer-max-size 0)
       (with-current-buffer gnuplot-buffer
-        (let (gnuplot-lines (count-lines (point-min) (point-max)))
+        (let ((gnuplot-lines (count-lines (point-min) (point-max))))
           (dotimes (tmp (- gnuplot-lines gnuplot-buffer-max-size))
             (goto-char (point-min))
             (delete-region (line-beginning-position) (1+ (line-end-position))))