Documentation change on coordinates parameter for slices()

Update to first line of docstring.

changed sub cubes to subcubes

Documentation change on coordinates parameter for slices()

Update to first line of docstring.

changed sub cubes to subcubes

Update to first line of docstring.

changed sub cubes to subcubes
Merge pull request #510 from munslowa/slices_documentation_update

Documentation change on coordinates parameter for slices()