title: Get `parse_date_time` to recognize single digit minutes
body: <p>I can't seem to find the right option for <code>lubridate</code>'s <code>parse_date_time</code> to recognize a single digit minute. Here is my use case.</p>
  
  <pre><code>library(lubridate)
  parse_date_time(hm("18 10"), "HMS")
  #[1] "0000-01-01 18:10:00 UTC"
  parse_date_time(hm("18 09"), "HMS")
  #[1] NA
  #Warning message:
  #All formats failed to parse. No formats found.
  </code></pre>
  
  <p>More broadly, I'm trying to plot by time of day (stripping out the date), so if there's a better way to do this, I'd love to know.</p>