Nighlites not working

conda.exceptions.UnsatisfiableError: The following specifications were found to be in conflict:
  - bob-devel=2019.03.07 -> libpng==1.6.35=hbc83047_0
  - libpng[version='>=1.6.36,<1.7.0a0']

https://gitlab.idiap.ch/bob/bob.nightlies/-/jobs/159644 https://gitlab.idiap.ch/bob/bob.nightlies/-/jobs/159643

Guys, shall we pin libpng to 1.6 on and https://gitlab.idiap.ch/bob/bob.devtools/blob/master/bob/devtools/data/conda_build_config.yaml ?

ping @amohammadi @andre.anjos