Bump version to 6.8.15

Author: rjernst

.ci/bwcVersions

@@ -80,3 +80,4 @@ BWC_VERSION:
   - "6.8.11"
   - "6.8.12"
   - "6.8.13"
+  - "6.8.14"

buildSrc/version.properties

@@ -1,4 +1,4 @@
-elasticsearch     = 6.8.14
+elasticsearch     = 6.8.15
 lucene            = 7.7.3
 
 # optional dependencies

server/src/main/java/org/elasticsearch/Version.java

@@ -158,8 +158,9 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_6_8_12 = new Version(6081299, org.apache.lucene.util.Version.LUCENE_7_7_3);
     public static final Version V_6_8_13 = new Version(6081399, org.apache.lucene.util.Version.LUCENE_7_7_3);
     public static final Version V_6_8_14 = new Version(6081499, org.apache.lucene.util.Version.LUCENE_7_7_3);
+    public static final Version V_6_8_15 = new Version(6081599, org.apache.lucene.util.Version.LUCENE_7_7_3);
 
-    public static final Version CURRENT = V_6_8_14;
+    public static final Version CURRENT = V_6_8_15;
 
 
     private static final ImmutableOpenIntMap<Version> idToVersion;