XD-1934 Update SI Splunk Extension to 1.1 GA

* change `splunkVersion` from `1.2.0` to `1.3.0`
* change `springIntegrationSplunkVersion` from `1.1.0.M2` to `1.1.0.RELEASE`

Jira: https://jira.spring.io/browse/XD-1934