Update ci.yml

Author: ponnhide

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.9, "3.10", "3.11"]
+        python-version: ["3.10", "3.11", "3.12"]
     steps:
       - name: Checkout
         uses: actions/checkout@v3
@@ -27,7 +27,7 @@ jobs:
         run: |
           pip install -U pip
           pip install wheel seaborn
-          pip install plotnine==0.12.4
+          pip install plotnine==0.13.6
           pip install pytest pytest-cov
           pip install .