title: Dask Dataframe sum of column always returning scalar
body: <p>I've created a Dask Dataframe (called "df") and the column with index "11" has integer values:</p>
  
  <pre><code>In [62]: df[11]
  Out[62]:
  Dask Series Structure:
  npartitions=42
      int64
        ...
      ...
        ...
        ...
  Name: 11, dtype: int64
  Dask Name: getitem, 168 tasks
  </code></pre>
  
  <p>I'm trying to sum these with:</p>
  
  <pre><code>df[11].sum() 
  </code></pre>
  
  <p>I get <code>dd.Scalar&lt;series-..., dtype=int64&gt;</code> returned. Despite researching what this might mean I'm still at odds as to why I'm not getting a numerical value returned. How can I translate this into its numerical value? </p>