Docs: Updated current version

docs/reference/index.asciidoc

@@ -1,7 +1,7 @@
 [[elasticsearch-reference]]
 = Reference
 
-:version:   1.5.1
+:version:   1.5.2
 :branch:    1.5
 :jdk:       1.8.0_25
 :defguide:  https://www.elastic.co/guide/en/elasticsearch/guide/current