Update test matrix to test 8.2 and latest (currently 9.0) and update 8.x references to 9.x

Author: fantavlik

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
         java-version:
           - 1.8
         splunk-version:
-          - "8.0"
+          - "8.2"
           - "latest"
     runs-on: ${{ matrix.os }}
 

README.md

@@ -40,7 +40,7 @@ Here's what you need to get going with the Splunk SDK for Java.
 If you haven't already installed Splunk, download it
 [here](http://www.splunk.com/download). For more about installing and running
 Splunk and system requirements, see
-[Installing & Running Splunk](http://dev.splunk.com/view/SP-CAAADRV). The Splunk SDK for Java has been tested with Splunk Enterprise 8.0 and 8.2.0.
+[Installing & Running Splunk](http://dev.splunk.com/view/SP-CAAADRV). The Splunk SDK for Java has been tested with Splunk Enterprise 9.0 and 8.2.
 
 #### Splunk SDK for Java