Index not iterable in Pandas 0.25.0
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
import matplotlib.pyplot as plt

# Get graphs in the notebook:
%matplotlib inline

pd.show_versions()

df = pd.DataFrame({'A': [1, 2, 3, 4, 15, 20, 99]})

data = df['A']

plt.plot(data, (data.index.values + 1) / len(data))
plt.show()

plt.plot(data, (data.index + 1) / len(data))
plt.show()
```
#### Problem description
In Pandas 0.23.4 the percentiles in CDF graphs can be expressed as (data.index + 1) / len(data), but in Pandas 0.25.0 this has to be changed to (data.index.values + 1) / len(data). No distaster but lots of work to change in many scripts.
#### Expected Output
[two nice CDF plots]
#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.3.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.15.0-47-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.0
numpy            : 1.16.2
pytz             : 2019.2
dateutil         : 2.8.0
pip              : 19.2.2
setuptools       : 41.0.1
Cython           : 0.29.2
pytest           : 4.0.2
hypothesis       : None
sphinx           : 1.8.2
blosc            : None
feather          : None
xlsxwriter       : 1.1.2
lxml.etree       : 4.2.5
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10
IPython          : 7.2.0
pandas_datareader: None
bs4              : 4.6.3
bottleneck       : 1.2.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.2.5
matplotlib       : 3.0.2
numexpr          : 2.6.8
odfpy            : None
openpyxl         : 2.5.12
pandas_gbq       : None
pyarrow          : 0.11.1
pytables         : None
s3fs             : None
scipy            : 1.1.0
sqlalchemy       : 1.2.15
tables           : 3.4.4
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.1.2

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-5-4663fc04bafd> in <module>
     14 plt.show()
     15 
---> 16 plt.plot(data, (data.index + 1) / len(data))
     17 plt.show()

/opt/anaconda/anaconda3/lib/python3.7/site-packages/matplotlib/pyplot.py in plot(scalex, scaley, data, *args, **kwargs)
   2811     return gca().plot(
   2812         *args, scalex=scalex, scaley=scaley, **({"data": data} if data
-> 2813         is not None else {}), **kwargs)
   2814 
   2815 

/opt/anaconda/anaconda3/lib/python3.7/site-packages/matplotlib/__init__.py in inner(ax, data, *args, **kwargs)
   1808                         "the Matplotlib list!)" % (label_namer, func.__name__),
   1809                         RuntimeWarning, stacklevel=2)
-> 1810             return func(ax, *args, **kwargs)
   1811 
   1812         inner.__doc__ = _add_data_doc(inner.__doc__,

/opt/anaconda/anaconda3/lib/python3.7/site-packages/matplotlib/axes/_axes.py in plot(self, scalex, scaley, *args, **kwargs)
   1609         kwargs = cbook.normalize_kwargs(kwargs, mlines.Line2D._alias_map)
   1610 
-> 1611         for line in self._get_lines(*args, **kwargs):
   1612             self.add_line(line)
   1613             lines.append(line)

/opt/anaconda/anaconda3/lib/python3.7/site-packages/matplotlib/axes/_base.py in _grab_next_args(self, *args, **kwargs)
    391                 this += args[0],
    392                 args = args[1:]
--> 393             yield from self._plot_args(this, kwargs)
    394 
    395 

/opt/anaconda/anaconda3/lib/python3.7/site-packages/matplotlib/axes/_base.py in _plot_args(self, tup, kwargs)
    376             func = self._makefill
    377 
--> 378         ncx, ncy = x.shape[1], y.shape[1]
    379         if ncx > 1 and ncy > 1 and ncx != ncy:
    380             cbook.warn_deprecated("2.2", "cycling among columns of inputs "

IndexError: tuple index out of range

</details>
