Update travis CI config to test against Splunk 6.4 and 6.5

Author: Shakeel Mohamed

.travis.yml

@@ -30,8 +30,8 @@ before_install:
     - mkdir -p $SPLUNK_HOME/var/log/splunk
 
 env:
-    - SPLUNK_VERSION=6.2.6-sdk
-    - SPLUNK_VERSION=6.3.1-sdk
+    - SPLUNK_VERSION=6.4-sdk
+    - SPLUNK_VERSION=6.5-sdk
 
 language: python