Fixed error in specification of OpenMM build platform for OS X.
Fixed error in specification of OpenMM build platform for OS X.


Former-commit-id: 8ee1338272ec3d7a919b61cf9c20b85a15cdf169
marscher/omnia-conda-recipes,peastman/conda-recipes,rmcgibbo/conda-recipes,jchodera/conda-recipes,rmcgibbo/conda-recipes,jchodera/conda-recipes,swails/conda-recipes,marscher/omnia-conda-recipes,omnia-md/conda-recipes,mpharrigan/conda-recipes,swails/conda-recipes,cwehmeyer/conda-recipes,omnia-md/conda-recipes,omnia-md/conda-recipes,danielparton/omnia-md-conda-recipes,mpharrigan/conda-recipes,peastman/conda-recipes,jchodera/conda-recipes,jchodera/conda-recipes,rmcgibbo/conda-recipes,cwehmeyer/conda-recipes,peastman/conda-recipes,swails/conda-recipes,cwehmeyer/conda-recipes,marscher/omnia-conda-recipes,rmcgibbo/conda-recipes,marscher/omnia-conda-recipes,mpharrigan/conda-recipes,danielparton/omnia-md-conda-recipes,swails/conda-recipes,cwehmeyer/conda-recipes