title: use get_as_dataframe to read google_speadsheet
body: <p>I used get_as_dataframe to read google spreadsheets which is very similar to excel. column A are float numbers, the sum of column B, C and D.   A2 =B2+C2+D2. when I use 'get_as_dataframe' to read the spreadsheets as dataframe, the value of column A is not a float number but the str of the equation '=B2+C2+D2'.
  how to fix this?
  thanks</p>
  
  <pre><code>from gspread_dataframe import get_as_dataframe, set_with_dataframe
  df = get_as_dataframe(sh.worksheet('sheetname'), parse_dates=True)
  </code></pre>