Bump cloudpickle from 1.5.0 to 1.6.0 (glotaran#402)

Bumps [cloudpickle](https://github.com/cloudpipe/cloudpickle) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/cloudpipe/cloudpickle/releases)
- [Changelog](https://github.com/cloudpipe/cloudpickle/blob/master/CHANGES.md)
- [Commits](cloudpipe/cloudpickle@v1.5.0...v1.6.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev.txt

@@ -9,7 +9,7 @@ bump2version>=0.5.11
 numpy==1.19.1
 scipy==1.5.2
 click==7.1.2
-cloudpickle==1.5.0
+cloudpickle==1.6.0
 dask[bag]==2.23.0
 lmfit==1.0.0
 numba==0.51.1