Increment version to 3.1.0-SNAPSHOT (opensearch-project#1517)

Signed-off-by: opensearch-ci-bot <[email protected]>
Co-authored-by: opensearch-ci-bot <[email protected]>
Co-authored-by: Peter Zhu <[email protected]>

Author: 3 people

build.gradle

@@ -20,7 +20,7 @@ import org.opensearch.gradle.testclusters.OpenSearchCluster
 
 buildscript {
     ext {
-        opensearch_version = System.getProperty("opensearch.version", "3.0.0-beta1-SNAPSHOT")
+        opensearch_version = System.getProperty("opensearch.version", "3.1.0-SNAPSHOT")
         isSnapshot = "true" == System.getProperty("build.snapshot", "true")
         buildVersionQualifier = System.getProperty("build.version_qualifier", "")
         version_tokens = opensearch_version.tokenize('-')