Bug in eda_scr using slow method

[Fegalf]

Hi,

I think there might be a problem in eda_scr function when used with method='slow' parameter. Here's a MWE (along with some data eda_example_1000hz.zip) and the traceback of the resulting error:

import pickle
import numpy as np 
import neurokit as nk

# Loading EDA as numpy array. 
with open('eda_example_1000hz.pkl', 'rb') as f: 
    eda = pickle.load(f)

# Extract SCR responses from EDA using slow method.
nk.bio_eda.eda_scr(eda, method='slow')

Which, in my case, raises the following error:

---------------------------------------------------------------------------`
TypeError                                 Traceback (most recent call last)
<ipython-input-98-6796372979af> in <module>()
     11 
     12 # Extract SCR responses from EDA using slow method.
---> 13 nk.bio_eda.eda_scr(eda, method='slow')

~\Anaconda3\envs\funii-env\lib\site-packages\neurokit\bio\bio_eda.py in eda_scr(signal, sampling_rate, treshold, method)
    404 
    405     # Keep only pairs
--> 406     peaks = peaks[peaks > onsets[0]]
    407     onsets = onsets[onsets < peaks[-1]]
    408 

TypeError: only integer scalar arrays can be converted to a scalar index

It seems that this problem is caused by an indexing method which only works with numpy arrays, and converting peaks and onsets variables to numpy array should fix this. https://github.com/neuropsychology/NeuroKit.py/blob/fb0fa99f2a2304b91f04ebc43cf551ce3cec95a3/neurokit/bio/bio_eda.py#L406-L407