Fixed an issue with passing pandas DataFrame as a parameter

[Mottl]

Fixed an issue with passing pandas DataFrame object as a symbols parameter for Moex data connector:

import pandas as pd
import pandas_datareader.data as web

symbols = pd.DataFrame(index=['SBER', 'USD000UTSTOM'])
df = web.DataReader(symbols, 'moex',
                    start='2017-07-01', end='2017-07-31')

[bashtage]

Could you add a whats new for this bug?

[Mottl]

There is a statement in whatsnew already about multiple symbols in a constructor:

- MOEX data connector now supports multiple symbols in a constructor.

I doubt we should add something more, because this is just a patch for this topic.