"ValueError: Percentiles must be in the range [0, 100]"

[mathause]

MCVE Code Sample

import xarray as xr
da = xr.DataArray([0, 1, 2])
da.quantile(q=50)

>>> ValueError: Percentiles must be in the range [0, 100]

Expected Output

ValueError: Quantiles must be in the range [0, 1]

Problem Description

By wrapping np.nanpercentile (xref: #3559) we also get the numpy error. However, the error message is wrong as xarray needs it to be in 0..1.

BTW: thanks for #3559, makes my life easier!

Output of xr.show_versions()

---

Edit: uses nanpercentile internally.

INSTALLED VERSIONS

commit: None
python: 3.7.3 | packaged by conda-forge | (default, Jul 1 2019, 21:52:21)
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 4.12.14-lp151.28.36-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.7.1

xarray: 0.14.1+28.gf2b2f9f6 (current master)
pandas: 0.25.2
numpy: 1.17.3
scipy: 1.3.1
netCDF4: 1.5.3
pydap: None
h5netcdf: 0.7.4
h5py: 2.10.0
Nio: None
zarr: None
cftime: 1.0.4.2
nc_time_axis: 1.2.0
PseudoNetCDF: None
rasterio: 1.1.1
cfgrib: None
iris: None
bottleneck: 1.2.1
dask: 2.6.0
distributed: 2.6.0
matplotlib: 3.1.2
cartopy: 0.17.0
seaborn: 0.9.0
numbagg: None
setuptools: 41.4.0
pip: 19.3.1
conda: None
pytest: 5.2.2
IPython: 7.9.0
sphinx: 2.2.1

[crusaderky]

Looks straightforward - could you open a PR?