title: R adding month over DST with lubridate gives unexpected result
body: <p>I get an unexpected result when adding a month over a DST period. I would expected the result to be "2018-11-01 GMT". When I run this code on Windows I get the correct result, however when I run the same thing on Red Hat Server the month is not added, see below.    </p>
  
  <pre><code>&gt; d = as.POSIXct('2018-10-01 00:00:00', tz = 'Europe/London')
  &gt; d + months(1)
  [1] "2018-10-01 BST"
  </code></pre>
  
  <p>Anyone has an idea of what is going on? </p>