consistency in plain template (code block options)

[nicholasjhorton]

First code block doesn't use , as separator

```{r include=FALSE}

but second one does

```{r, include=FALSE}

I don't care which format we use as long as we are consistent.

[rpruim]

For lack of a better rule, I looked in one of Hadley's vignettes. He uses the comma, so I'll go that way too.