title: pandas.Int64Index fix for FutureWarning
body: <p>Just getting this new warning for my dataframes that are loaded from excel.</p>
  <p>I understand if I were to pd.DataFrame I could set the index, but I am not clear how to set the dataframe index type when I am loading from a file.</p>
  <p>C:\python\python38\lib\site-packages\geopandas\io\file.py:362: FutureWarning: pandas.Int64Index is deprecated and will be removed from pandas in a future version. Use pandas.Index with the appropriate dtype instead.</p>
  <p>Excerpt from class:</p>
  <pre><code>xls = pd.ExcelFile('C:/QGISwork/generic_templates/fielddbtemplate_db.xlsx')
          self.header = xls.parse('generic', header = None)
          self.df = xls.parse('generic', skiprows=4, index_col=0, na_values=['NA'])
  </code></pre>