Drop 3.7 support and upgrade pandas

New pandas requires a newer python version. Since Ubuntu 20.04
the default Python verseion is 3.8.

The old pandas depends on a numpy version which has a security
vulnerability.

Author: rrooij

.github/workflows/python.yml

@@ -31,7 +31,7 @@ jobs:
       TERMINUSX_TOKEN: ${{ secrets.TERMINUSX_TOKEN_DEV }}
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10"]
+        python-version: ["3.8", "3.9", "3.10"]
 
     steps:
     - uses: actions/checkout@v2