MNT:(deps): Bump xarray from 0.15.1 to 0.16.0 in /ci

Bumps [xarray](https://github.com/pydata/xarray) from 0.15.1 to 0.16.0.
- [Release notes](https://github.com/pydata/xarray/releases)
- [Changelog](https://github.com/pydata/xarray/blob/master/HOW_TO_RELEASE.md)
- [Commits](pydata/xarray@v0.15.1...v0.16.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

ci/Current.txt

@@ -2,7 +2,7 @@ matplotlib==3.2.1
 numpy==1.18.5
 scipy==1.5.2
 pint==0.14
-xarray==0.15.1
+xarray==0.16.0
 traitlets==4.3.3
 pooch==1.1.1
 pandas==1.0.5