title: The fig file was inculded in function include_graphics(), could lost file extension when rmd to pdf/tex
body: <p>I get a problem when I use knit to convert rmd to pdf, as follow：</p>
  <p><strong>rcode in my .rmd like this:</strong></p>
  <pre><code>
  knitr::include_graphics('image/xyzAnovaFig.svg')
  </code></pre>
  <p><strong>The result of rmd-&gt;tex/pdf is</strong>:</p>
  <pre><code>\begin{figure}
  
  {\centering \includegraphics[width=0.7\linewidth]{image/xyzAnovaFig} 
  
  }
  
  \caption{MSb,MSw Example}\label{fig:xyzanova1}
  \end{figure}
  </code></pre>
  <p>As you can see, the suffix of the picture will be lost, causing the picture not to be displayed in the pdf and compilation errors.</p>
  <p>How can i fix it? Please.</p>