Fix that `print` command raises `FrozenError` in `mrdb`; ref 1f5a7f2f

#### Before this patch:

  ```
  $ echo 'p true' | bin/mrdb /dev/null
  (/dev/null:1) mruby application exited.
  FrozenError: can't modify frozen String
  (-:0)
  ```

#### After this patch:

  ```
  $ echo 'p true' | bin/mrdb /dev/null
  (/dev/null:1) $1 = true
  (/dev/null:1)
  ```

1 files changed, 1 insertions, 1 deletions

diff --git a/mrbgems/mruby-bin-debugger/tools/mrdb/apiprint.c b/mrbgems/mruby-bin-debugger/tools/mrdb/apiprint.c
index cdd7b6fa6..e8702f4df 100644
--- a/mrbgems/mruby-bin-debugger/tools/mrdb/apiprint.c
+++ b/mrbgems/mruby-bin-debugger/tools/mrdb/apiprint.c
@@ -74,7 +74,7 @@ mrb_debug_eval(mrb_state *mrb, mrb_debug_context *dbg, const char *expr, size_t
     *exc = mrb_obj_is_kind_of(mrb, v, mrb->eException_class);
   }
 
-  s = mrb_funcall(mrb, v, "inspect", 0);
+  s = mrb_inspect(mrb, v);
 
   /* enable code_fetch_hook */
   mrb->code_fetch_hook = tmp;