Update .travis.yml to skip 7.x

Author: jsvd

.travis.yml

@@ -1,9 +1,8 @@
 import:
-  - logstash-plugins/.ci:travis/[email protected]
-  - logstash-plugins/.ci:travis/[email protected]
+  - logstash-plugins/.ci:travis/[email protected]
 
-env:
-  jobs:
-    # lock on version 8.x because use of Jackson 2.13.3 available from 8.3.0
-    - ELASTIC_STACK_VERSION=8.x DOCKER_ENV=dockerjdk17.env
-    - SNAPSHOT=true ELASTIC_STACK_VERSION=8.x DOCKER_ENV=dockerjdk17.env
+# lock on version 8.x because use of Jackson 2.13.3 available from 8.3.0
+jobs:
+  exclude:
+  - env: ELASTIC_STACK_VERSION=7.current
+  - env: SNAPSHOT=true ELASTIC_STACK_VERSION=7.current