title: ERROR: dependency 'ROracle' is not available for package 'ora'
body: <p>I´m try to install "ora" package, so I use this command: </p>
  
  <pre><code>install.packages("ora")
  </code></pre>
  
  <p>However, it throws me the following error, where it indicates that the version of ROracle is not viable. </p>
  
  <pre><code>installing the source package 'ora'
    trying URL 'https://cran.rstudio.com/src/contrib/ora_2.0-1.tar.gz'
    Content type 'application/x-gzip' length 5815 bytes
    downloaded 5815 bytes
  
  ERROR: dependency 'ROracle' is not available for package 'ora'
  * removing 'C:/Users/samora/Documents/R/R-3.5.1/library/ora'
  In R CMD INSTALL
  Warning in install.packages :
    installation of package ‘ora’ had non-zero exit status
  
  The downloaded source packages are in
      ‘C:\Users\samora\AppData\Local\Temp\RtmpIxcR0T\downloaded_packages’
  </code></pre>
  
  <p>So I try to update it, but still after doing so, continue with the error.</p>
  
  <p>Could you help me?</p>