kde.py: ValueError: `dataset` input should have multiple elements.

[sbentt]

Hi,
I'm having an issue with VESPA, when it tries to perform the Gaussian kernel density estimate. It seems that the problem is not with the routine, but with the data the routine analyses.
When I run calcfpp I get:

`Traceback (most recent call last):

File "/Users/sb/miniconda3/bin/calcfpp", line 66, in
from vespa import FPPCalculation
File "/Users/sb/miniconda3/lib/python3.6/site-packages/vespa/init.py", line 22, in
from .stars.populations import StarPopulation
File "/Users/sb/miniconda3/lib/python3.6/site-packages/vespa/stars/init.py", line 1, in
from .populations import StarPopulation
File "/Users/sb/miniconda3/lib/python3.6/site-packages/vespa/stars/populations.py", line 54, in
from .utils import randpos_in_circle, draw_raghavan_periods
File "/Users/sb/miniconda3/lib/python3.6/site-packages/vespa/stars/utils.py", line 33, in
RAGHAVAN_BINPERKDE = KDE_Distribution(RAGHAVAN_BINPERS,adaptive=False)
File "/Users/sb/miniconda3/lib/python3.6/site-packages/simpledist/distributions.py", line 1039, in init
bandwidth=bandwidth)
File "/Users/sb/miniconda3/lib/python3.6/site-packages/simpledist/kde.py", line 104, in init
self.gauss_kde = gaussian_kde(self.dataset,bw_method=bandwidth,**kwargs)
File "/Users/sb/miniconda3/lib/python3.6/site-packages/scipy/stats/kde.py", line 195, in init
raise ValueError("dataset input should have multiple elements.")
ValueError: dataset input should have multiple elements.`

I thought it could be related to the isochrones models I ran earlier, but the same error occurs when I run the code in the example directory of kepler-22.
I'm using VESPA 0.6 and isochrones 1.2.2 (not 2.0.1, as you suggested in #29, but I have the same problem with both the releases).
Any help would be appreciated.
Thank you