bump version to 6.8.8 (elastic#53019)

Author: jakelandis

.ci/bwcVersions

@@ -73,3 +73,4 @@ BWC_VERSION:
   - "6.8.4"
   - "6.8.5"
   - "6.8.6"
+  - "6.8.7"

buildSrc/version.properties

@@ -1,4 +1,4 @@
-elasticsearch     = 6.8.7
+elasticsearch     = 6.8.8
 lucene            = 7.7.2
 
 # optional dependencies

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

@@ -151,8 +151,9 @@ public class Version implements Comparable<Version>, ToXContentFragment {
     public static final Version V_6_8_5 = new Version(6080599, org.apache.lucene.util.Version.LUCENE_7_7_2);
     public static final Version V_6_8_6 = new Version(6080699, org.apache.lucene.util.Version.LUCENE_7_7_2);
     public static final Version V_6_8_7 = new Version(6080799, org.apache.lucene.util.Version.LUCENE_7_7_2);
+    public static final Version V_6_8_8 = new Version(6080899, org.apache.lucene.util.Version.LUCENE_7_7_2);
 
-    public static final Version CURRENT = V_6_8_7;
+    public static final Version CURRENT = V_6_8_8;
 
 
     private static final ImmutableOpenIntMap<Version> idToVersion;