Fix 0-dimensional arrays accessed via netCDF4-python

netCDF4-python has a bug (for which I've submitted a PR) that means that the
data from a 0-dimensional array is always returned as a 1-dimensional array:
https://github.com/Unidata/netcdf4-python/pull/220
Merge pull request #35 from akleeman/fix-0d-netCDF4-variables

Fix 0-dimensional arrays accessed via netCDF4-python