Use non-buggy CDO in Dockerfile

[jonasjucker]

See C2SM/zonda-request#59

Unfortunately for ubuntu:latest, only cdo 2.4.0 is available.

[mjaehn]

Could we install the latest cdo (2.5.0) manually? https://code.mpimet.mpg.de/news/543
Unfortunately, it is not (yet) available via conda-forge: https://anaconda.org/conda-forge/cdo