[openmmtools] fix py3 issue in installation
[openmmtools] fix py3 issue in installation

cwehmeyer/conda-recipes,swails/conda-recipes,swails/conda-recipes,cwehmeyer/conda-recipes,cwehmeyer/conda-recipes,cwehmeyer/conda-recipes,omnia-md/conda-recipes,jchodera/conda-recipes,omnia-md/conda-recipes,omnia-md/conda-recipes,swails/conda-recipes,jchodera/conda-recipes,swails/conda-recipes,jchodera/conda-recipes,peastman/conda-recipes,peastman/conda-recipes,peastman/conda-recipes,jchodera/conda-recipes