title: Warning message at R startup (slidify, rmarkdown)
body: <p>When I startup my R (in RStudio IDE), I receive the warning:</p>
  
  <blockquote>
    <p>Warning: namespace ‘slidify’ is not available and has been replaced by
    .GlobalEnv when processing object ‘.SLIDIFY_ENV’</p>
  </blockquote>
  
  <p>Yesterday I uninstalled <code>slidify</code> (and <code>slidifyLibraries</code>) as this package interfered with regular use or <code>.Rmd</code> (Rmarkdown) files (when I pushet <code>knit</code> button in RStudio, all the .Rmd files were rendered as <code>slidify</code> slides, despite the fact that they had to be rendered as usual Rmarkdown files).</p>
  
  <p><strong>Question:</strong> How can I get rid of the warning message at the startup?</p>