title: R, issue "unable to load shared object cairo.so" on Linux CentOS 7
body: <p>I've been using R with ggplot2 and other packages on my Linux CentOS 7 for a long time.
  Today, all of a sudden, it stopped working.</p>
  
  <p>When I call the <code>png()</code> function in my script, it generates the following errrors:</p>
  
  <pre><code>Warning messages:
  1: In png(heatmap_file) :
    unable to load shared object '/usr/lib64/R/library/grDevices/libs//cairo.so':
    /lib64/libcairo.so.2: undefined symbol: FT_Get_Var_Design_Coordinates
  2: In png(heatmap_file) : failed to load cairo DLL
  </code></pre>
  
  <p>I tried to update the cairo package many times but nothing worked out so far.
  What can I do?</p>
  
  <p>Thanks!</p>