Use newer version of Pillow for min-versions CI test

Pillow-6.1.0 is refusing to install for Python-3.8, so update to 7.2.0.

Author: johnomotani

.github/workflows/pythonpackage.yml

@@ -55,7 +55,7 @@ jobs:
       matrix:
         python-version: [3.7, 3.8]
         pip-packages:
-          - "setuptools pip pytest pytest-cov coverage codecov boutdata==0.1.4 xarray==0.18.0 dask==2.10.0 numpy==1.18.0 natsort==5.5.0 matplotlib==3.1.1 animatplot==0.4.2 netcdf4==1.4.2 Pillow==6.1.0" # test with oldest supported version of packages. Note, using numpy==1.18.0 as a workaround because numpy==1.17.0 is not supported on Python-3.7, even though we should currently support numpy==1.17.0.
+          - "setuptools pip pytest pytest-cov coverage codecov boutdata==0.1.4 xarray==0.18.0 dask==2.10.0 numpy==1.18.0 natsort==5.5.0 matplotlib==3.1.1 animatplot==0.4.2 netcdf4==1.4.2 Pillow==7.2.0" # test with oldest supported version of packages. Note, using numpy==1.18.0 as a workaround because numpy==1.17.0 is not supported on Python-3.7, even though we should currently support numpy==1.17.0.
       fail-fast: false
 
     steps:

.github/workflows/pythonpublish.yml

@@ -49,7 +49,7 @@ jobs:
       matrix:
         python-version: [3.7, 3.8]
         pip-packages:
-          - "setuptools pip pytest pytest-cov coverage codecov boutdata==0.1.4 xarray==0.18.0 dask==2.10.0 numpy==1.18.0 natsort==5.5.0 matplotlib==3.1.1 animatplot==0.4.2 netcdf4==1.4.2 Pillow==6.1.0" # test with oldest supported version of packages. Note, using numpy==1.18.0 as a workaround because numpy==1.17.0 is not supported on Python-3.7, even though we should currently support numpy==1.17.0.
+          - "setuptools pip pytest pytest-cov coverage codecov boutdata==0.1.4 xarray==0.18.0 dask==2.10.0 numpy==1.18.0 natsort==5.5.0 matplotlib==3.1.1 animatplot==0.4.2 netcdf4==1.4.2 Pillow==7.2.0" # test with oldest supported version of packages. Note, using numpy==1.18.0 as a workaround because numpy==1.17.0 is not supported on Python-3.7, even though we should currently support numpy==1.17.0.
       fail-fast: true
 
     steps: