Here is the versions of pandas, numpy and matplotlib I'm using.
numpy 1.16.3 py37he5ce36f_0 conda-forge
matplotlib 3.1.0 py37_0 conda-forge
matplotlib-base 3.1.0 py37h5f35d83_0 conda-forge
pandas 0.24.2 py37hf484d3e_0 conda-forge
petropy 0.1.6 pypi_0 pypi
And here is what I'm getting:

Any help would be greatly appreciated.