[FLINK-37675] Update elastic.yml for 3.1.0 release

Author: reswqa

docs/data/elastic.yml

@@ -16,7 +16,8 @@
 # limitations under the License.
 ################################################################################
 
-version: 4.0.0-SNAPSHOT
+version: 3.1.0
+flink_compatibility: [1.18, 1.19, 1.20]
 variants:
   - maven: flink-connector-elasticsearch6
     sql_url: https://repo.maven.apache.org/maven2/org/apache/flink/flink-sql-connector-elasticsearch6/$full_version/flink-sql-connector-elasticsearch6-$full_version.jar