Bump the minimal required Python to 3.8

We discussed this at one of the recent coder calls; the motivation
includes better mypy type hint support, especially in numpy, but also in
the language core, and of course the dataclasses.

Change-Id: I8ffee28c33f167cbcba978c85486e58a1b8c99be

.travis.yml

@@ -3,8 +3,6 @@ os: linux
 language: python
 services: docker
 python:
-  - "3.6"
-  - "3.7"
   - "3.8"
   - "3.9"
 before_install:

.zuul.yaml

@@ -13,7 +13,6 @@
               coverage_job_name_current: tox-py38-cover
         - tox-linters-diff-n-report:
             voting: false
-        - tox-py36-el8
         - tox-docs-f32
         - tox-py38-cover-previous
     gate:

docs/install.rst

@@ -38,7 +38,7 @@ Using Python on your computer
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
    **Note**: `gnpy` supports Python 3 only. Python 2 is not supported.
-   `gnpy` requires Python ≥3.6
+   `gnpy` requires Python ≥3.8
 
    **Note**: the `gnpy` maintainers strongly recommend the use of Anaconda for
    managing dependencies.
@@ -84,7 +84,7 @@ exact version of Python you are using.
     $ which python                   # check which Python executable is used
     /path/to/anaconda/bin/python
     $ python -V                      # check your Python version
-    Python 3.6.5 :: Anaconda, Inc.
+    Python 3.8.0 :: Anaconda, Inc.
 
 .. _install-pip:
 

setup.cfg

@@ -10,7 +10,7 @@ home-page = https://github.com/Telecominfraproject/oopt-gnpy
 project_urls =
     Bug Tracker = https://github.com/Telecominfraproject/oopt-gnpy/issues
     Documentation = https://gnpy.readthedocs.io/
-python-requires = >=3.6
+python-requires = >=3.8
 classifier =
     Development Status :: 5 - Production/Stable
     Intended Audience :: Developers
@@ -20,8 +20,6 @@ classifier =
     Natural Language :: English
     Programming Language :: Python
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: Implementation :: CPython