Remove Python 3.7 from CI

Author: aaltat

.github/workflows/CI.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8]
+        python-version: [2.7, 3.6, 3.8]
         rf-version: [3.1.2, 3.2rc2]
 
     steps: