Tikz-CD in WriteLaTeX: Commutative Diagrams with Parallel Arrows

Tikz-CD in WriteLaTeX: Commutative Diagrams with Parallel Arrows

In writelatex, trying to get the first example on page six of this Tikz-cd
document to work. From this code:
\documentclass{beamer}
\usepackage{tikz,tikz-cd}
\usetikzlibrary{arrows,chains,matrix,positioning,scopes}
\begin{document}
\begin{frame}[fragile]{Tikz-cd}
\begin{tikzcd}
A \arrow[yshift=0.7ex]{r} \arrow[yshift=-0.7ex]{r}
& B \arrow[xshift=0.7ex]{d} \arrow[xshift=-0.7ex]{d} \\
& C
\end{tikzcd}
\end{frame}
\end{document}
I expect to see this

and instead see this