Appveyor-CI: Bump Python 3.6 -> 3.8
Appveyor-CI: Bump Python 3.6 -> 3.8

google/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,google/or-tools