R: knitrBootstrap in RStudio using YAML frontal fabric

Question

I am trying to compile knitrMWE using a package knitrBootstrap. I use the Ctrl+ Shift+ Kshortcut in RStudio, which essentially calls a function knitfrom knitr.

Here is the MWE I'm trying to compile, which is basically the MWE given on the Jim Hester knitrBootstrappage here :

---
author: "FG"
date: "Tuesday, April 29, 2014"
output:
  knitrBootstrap::bootstrap_document:
    title: "Test LaTeX"
    theme: journal
    highlight: visual studio
    theme.chooser: TRUE
    highlight.chooser: TRUE
---

```{r}
x = a + b
```

$$ 
\begin{align}
x^2 + \mathbf{y}^2
\end{align}
$$

However it gives me

Error: "bootstrap_document" is not an exported object from 'namespace: knitrBootstrap' Execution paused

What is bootstrap_documentnot a function exported from a namespace knitrBootstrapis easy to verify. Has anything changed since Jim Hester's blog page was written?