title: Cannot get Highcharter to plot time series
body: <p>Trying to plot some time series data with Highcharter</p>
  
  <p>The data is as the following:</p>
  
  <pre><code>time &lt;- c("2018-04-23 10:14:39 UTC", "2018-04-23 10:16:41 UTC", "2018-04-23 10:16:42 UTC", "2018-04-23 10:16:51 UTC", "2018-04-23 10:16:54 UTC", "2018-04-23 10:18:23 UTC")
  min &lt;- c(0.00020522, 0.00020520, 0.00020517, 0.00020500, 0.00020500, 0.00020522)
  max &lt;- c(0.00020527, 0.00020525, 0.00020517, 0.00020550, 0.00020500, 0.00020522)
  
  dff &lt;- data.frame(min, max) 
  dff$time &lt;- as.POSIXct(time)
  tib &lt;- as_tibble(dff)
  </code></pre>
  
  <p>All the code variants below produce "No data to display" message, same on Linux and Windows:</p>
  
  <pre><code>hchart(tib, type = "errorbar", hcaes(x = time, ymin = min, ymax = max))
  highchart() %&gt;% hc_add_series(tib, "errorbar", hcaes(x = time, ymin = min, ymax = max))
  hchart(tib, type = "errorbar", hcaes(x = datetime_to_timestamp(time), ymin = min, ymax = max))
  highchart() %&gt;% hc_add_series(tib, "errorbar", hcaes(x = datetime_to_timestamp(time), ymin = min, ymax = max))
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>Was able to plot <code>"line"</code> by transforming the time variable with <code>datetime_to_timestamp</code> as advised <a href="https://stackoverflow.com/questions/41573626/highcharter-plotbands-plotlines-with-time-series-data">here</a>:</p>
  
  <pre><code>highchart() %&gt;% hc_add_series(tib, "line", hcaes(x = datetime_to_timestamp(time), y = min))
  hchart(tib, type = "line", hcaes(x = datetime_to_timestamp(time), y = min))
  </code></pre>
  
  <p>At the same time, the error bar <code>ggplot</code> code works fine:</p>
  
  <pre><code>ggplot() +   geom_errorbar(data = tib, aes(x = time, ymin = min, ymax = max))
  </code></pre>