Support `NODE_LITERAL_DELIM` in `mrb_parser_dump`

#### Before this patch:

  ```terminal
  $ bin/mruby -v -e '%w[1 2]'
  mruby 2.0.1 (2019-04-04)
  00001 NODE_SCOPE:
  00001   NODE_BEGIN:
  00001     NODE_WORDS:
  00001       NODE_STR "1" len 1
  00001       node type: 85 (0x55)
  00001       NODE_STR "2" len 1
  (snip)
  ```

#### After this patch:

  ```terminal
  $ bin/mruby -v -e '%w[1 2]'
  mruby 2.0.1 (2019-04-04)
  00001 NODE_SCOPE:
  00001   NODE_BEGIN:
  00001     NODE_WORDS:
  00001       NODE_STR "1" len 1
  00001       NODE_LITERAL_DELIM
  00001       NODE_STR "2" len 1
  (snip)
  ```

mrbgems/mruby-compiler/core/parse.y

@@ -6950,6 +6950,10 @@ mrb_parser_dump(mrb_state *mrb, node *tree, int offset)
     dump_recur(mrb, tree, offset+1);
     break;
 
+  case NODE_LITERAL_DELIM:
+    printf("NODE_LITERAL_DELIM\n");
+    break;
+
   case NODE_SELF:
     printf("NODE_SELF\n");
     break;