Increment version to 2.13.1-SNAPSHOT

Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>

Author: opensearch-ci-bot

build.gradle

@@ -18,7 +18,7 @@ buildscript {
     ext {
         opensearch_group = "org.opensearch"
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
-        opensearch_version = System.getProperty("opensearch.version", "2.13.0-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "2.13.1-SNAPSHOT")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
         // 2.3.0-SNAPSHOT -> 2.3.0.0-SNAPSHOT
         version_tokens = opensearch_version.tokenize('-')