title: Valid time zones in lubridate
body: <p>A quick google search seems to get me nowhere. What are valid time zones in lubridate's <code>tz</code> option? In particular, am looking for Brasilia's time zone. Thanks!</p>
  
  <pre><code>library(lubridate)
  dts &lt;- c("6-3-1995 12:01:01","29-3-1995 23:01:01","29-3-1995 20:01:01")
  dmy_hms(dts)               # locale's tz default
  dmy_hms(dts, tz = "chile") # Chilean time (has one time zone only)
  </code></pre>