Emacs: reset buffer configuration when stopping the merlin server

Otherwise, restarting the server after changing merlin-command has no
effect, because the old value for merlin-command is cached in
merlin-buffer-configuration.

emacs/merlin.el

@@ -571,6 +571,11 @@ return (LOC1 . LOC2)."
   (unless merlin-mode (message "Buffer is not managed by merlin."))
   (when merlin-mode
     (merlin--call-merlin "stop-server")
+    ;; `merlin-buffer-configuration' is buffer-local, so reset it in
+    ;; all buffers.
+    (dolist (buf (buffer-list))
+      (with-current-buffer buf
+        (kill-local-variable 'merlin-buffer-configurationn)))
     (setq merlin-erroneous-buffer nil)
     (setq merlin-buffer-configuration nil)))