requirements:run: did not install "gsl" Conda package on OSX Python 3.6

conda-build-issue.md

Actual Behavior

On OSX (Python3.6) conda-build did not install "gsl" package with this meta.yaml, although "gsl" is described in requirements: run:

https://travis-ci.org/ecell/ecell4_base/jobs/556201206#L2960

Expected Behavior

## Package Plan ##
  environment location: /Users/travis/miniconda/conda-bld/ecell4_base_1562667636299/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_pla
The following NEW packages will be INSTALLED:
    appnope:           0.1.0-py36hf537a9a_0          
    attrs:             19.1.0-py36_1                 
    backcall:          0.1.0-py36_0                  
    bleach:            3.1.0-py36_0                  
    bzip2:             1.0.7-h1de35cc_0              
    ca-certificates:   2019.5.15-0                   
    certifi:           2019.6.16-py36_0              
    decorator:         4.4.0-py36_1                  
    defusedxml:        0.6.0-py_0                    
    ecell4_base:       2.0.0b3-py36_18_ge214bd2 local
    entrypoints:       0.3-py36_0                    
    ffmpeg:            4.0-h01ea3c9_0                
    freetype:          2.9.1-hb4e5f40_0              
    gsl:             2.4-h1de35cc_4 
    hdf5:              1.10.4-hfa1e0ec_0             
    ipykernel:         5.1.1-py36h39e3cac_0          
    ipython:           7.6.0-py36h39e3cac_0          
    ipython_genutils:  0.2.0-py36h241746c_0          
    jedi:              0.13.3-py36_0                 

Steps to Reproduce

Restart this TravisCI build (but you can not control this...).

Output of conda info