build(deps): bump cloudpickle from 1.1.1 to 1.2.1

Bumps [cloudpickle](https://github.com/cloudpipe/cloudpickle) from 1.1.1 to 1.2.1.
- [Release notes](https://github.com/cloudpipe/cloudpickle/releases)
- [Changelog](https://github.com/cloudpipe/cloudpickle/blob/master/CHANGES.md)
- [Commits](cloudpipe/cloudpickle@v1.1.1...v1.2.1)

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

requirements.txt

@@ -1,6 +1,6 @@
 certifi==2019.3.9
 chardet==3.0.4
-cloudpickle==1.1.1
+cloudpickle==1.2.1
 cycler==0.10.0
 dask==1.2.2
 decorator==4.4.0