pandas FutureWarning

[gandy92]

With current pandas, there is a FutureWarning triggered by line 607 in ``pykrakenapi.py:

.../venv/lib/python3.8/site-packages/pykrakenapi/pykrakenapi.py:607: FutureWarning: In a future version, `df.iloc[:, i] = newvals` will attempt to set the values inplace instead of always setting a new array. To retain the old behavior, use either `df[df.columns[i]] = newvals` or, if columns are non-unique, `df.isetitem(i, newvals)`
  ohlc.loc[:, col] = ohlc[col].astype(float)

A working solution is to replace

for col in ['open', 'high', 'low', 'close', 'vwap', 'volume']:
    ohlc.loc[:, col] = ohlc[col].astype(float)

with

ohlc = ohlc.astype({name: float for name in ['open', 'high', 'low', 'close', 'vwap', 'volume']})

There are more similar lines like this that will require fixing.