be more explicit about supported python versions

Author: nschloe

.github/workflows/ci.yml

@@ -9,10 +9,9 @@ jobs:
     - uses: actions/setup-python@v1
       with:
         python-version: "3.x"
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Lint with flake8
       run: |
-        pip install --upgrade pip
         pip install flake8
         flake8 .
     - name: Lint with black
@@ -22,16 +21,18 @@ jobs:
 
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
     steps:
     - uses: actions/setup-python@v1
       with:
         python-version: "3.x"
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Install dependencies
       run: sudo apt-get install -y texlive-latex-base texlive-latex-extra context python3-tk
     - name: Install package
       run: |
-        pip install --upgrade pip
         pip install .
     - name: Extract tests from README
       run: |

README.md

@@ -7,6 +7,7 @@
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg?style=flat-square)](https://github.com/psf/black)
 [![Documentation Status](https://readthedocs.org/projects/tikzplotlib/badge/?version=latest&style=flat-square)](https://readthedocs.org/projects/tikzplotlib/?badge=latest)
 [![awesome](https://img.shields.io/badge/awesome-yes-brightgreen.svg?style=flat-square)](https://github.com/nschloe/tikzplotlib)
+[![PyPI pyversions](https://img.shields.io/pypi/pyversions/tikzplotlib.svg?style=flat-square)](https://pypi.org/pypi/tikzplotlib/)
 [![PyPi Version](https://img.shields.io/pypi/v/tikzplotlib.svg?style=flat-square)](https://pypi.org/project/tikzplotlib)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.1173089.svg?style=flat-square)](https://doi.org/10.5281/zenodo.1173089)
 [![GitHub stars](https://img.shields.io/github/stars/nschloe/tikzplotlib.svg?style=flat-square&logo=github&label=Stars&logoColor=white)](https://github.com/nschloe/tikzplotlib)

setup.py

@@ -26,8 +26,10 @@
         about["__status__"],
         about["__license__"],
         "Operating System :: OS Independent",
-        "Programming Language :: Python",
         "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Topic :: Multimedia :: Graphics :: Graphics Conversion",
         "Topic :: Scientific/Engineering :: Visualization",
     ],