title: measurements::conv_unit() returns character vector where numeric expected
body: <p>Based on <a href="https://stackoverflow.com/questions/14404596/converting-geo-coordinates-from-degree-to-decimal">this question</a> and related, I am using measurements::conv_unit() to convert Degree:Min:Sec coordinates to decimal.<br>
  However, whilst of correct 'value', my return is a character vector, not numeric as should be according to all I've seen elsewhere. 
  My input is character as per per <code>?measurements::conv_unit : "Coordinate: Values must be entered as a string with one space between subunits (e.g. 70° 33’ 11” = "70 33 11")."</code>  </p>
  
  <p>Example:</p>
  
  <pre><code>df &lt;- c("1 1 1", "-1 1 1", "2 2 2","-2 2 2")  
  
  measurements::conv_unit(df, from = 'deg_min_sec', to = 'dec_deg')
  [1] "1.01694444444444"  "-1.01694444444444" "2.03388888888889"  "-2.03388888888889"
  </code></pre>
  
  <p>The conversion to numeric (via as.numeric()) is of course a simple solution, but this shouldn't be needed in the first place I believe.
  The result is same whether I define df as c(), data.frame() or tibble(), and even when above is run in a clean (restarted) R session.
  Measurements version 1.1.0, installed just today.</p>
  
  <p>Am I doing something wrong or what's happening?</p>