plot_years with a size 1 "show" dimension

[jucordero]

matplotlib complains when trying to generate a plot_years plot on a DataArray with a size-1 named dimension and using it as the "show" parameter.

To reproduce the error:

from agrifoodpy.food.food import FoodElementSheet
import xarray as xr
import numpy as np

da_1 = xr.DataArray(np.random.rand(5,1),
                        coords=[('Year', [2010, 2011, 2012, 2013, 2014]),
                                ('Region', ['A'])],
                        dims=['Year', 'Region'])
fbs_1 = FoodElementSheet(da_1)

fbs_1.plot_years(show="Region")

I tried using da.squeeze() to remove size-1 named dimension and it does seems to fix the issue.