title: Round a range in pandas
body: <p>I have df_surf_dist=</p>
  <pre><code>                 index  surface_relle_bati
  0      (8.718, 27.733]                 442
  1     (27.733, 46.467]                1485
  2       (46.467, 65.2]                1296
  3       (65.2, 83.933]                 927
  4    (83.933, 102.667]                 288
  5     (102.667, 121.4]                  81
  6     (121.4, 140.133]                  22
  7   (140.133, 158.867]                   8
  8     (158.867, 177.6]                  10
  9     (177.6, 196.333]                   1
  10  (196.333, 215.067]                   1
  11    (215.067, 233.8]                   1
  12    (233.8, 252.533]                   0
  13  (252.533, 271.267]                   0
  14    (271.267, 290.0]                   1
  </code></pre>
  <p>I want to round the range in order to plot it and make the scale look nice.</p>
  <p>I tried <code>df_surf_dist.index.round(decimals=-1)</code></p>
  <p>but I got <code>AttributeError: 'RangeIndex' object has no attribute 'round'</code></p>
  <p>I also tried <code>df_surf_dist.index = df_surf_dist.index.to_series().apply(lambda x: x.round(1))</code></p>
  <p>but I got <code>AttributeError: 'int' object has no attribute 'round'</code></p>