Won't work with attr.source='.numberLines' in r chunk?

[tanduc307]

Dear developers of flair package,
This is a great tool for highlighting source code R that useful for training new R users. This is what I am looking for!! Thanks for creating it! Anyway, here is my issue:

First, I highlight code

{r, echo=TRUE}

decorate("code_1") %>%
  flair_lines(2)

it works OK in this example

{r code_1, echo=TRUE, warning=FALSE, message=FALSE, include=FALSE}

iris %>%
  group_by(Species) %>%
  summarize(mean(Sepal.Length))

but it not works if I add attr.source='.numberLines' in r chunk option of code_1
This is the error message:

Error in eval(x, envir = envir) : object '.numberLines' not found
Calls: <Anonymous> ... eval_lang -> in_input_dir -> in_dir -> eval -> eval
Execution halted

I hope my issue was clearly presented. Hoping this can be solved.
Regards,
Duc