Add Splunk 8.1 to the test suite

Author: artemrys

.github/workflows/test.yml

@@ -13,6 +13,7 @@ jobs:
           - ubuntu-latest
         python: [ 2.7, 3.7 ]
         splunk-version:
+          - "8.1"
           - "8.2"
           - "latest"
       fail-fast: false