[DOCS] Fixed doctests attribute name to match.

docs/java-rest/index.asciidoc

@@ -1,7 +1,7 @@
 [[java-rest]]
 = Java REST Client
 
-:doctest:   {docdir}/../../client/rest-high-level/src/test/java/org/elasticsearch/client/documentation
+:doctests:   {docdir}/../../client/rest-high-level/src/test/java/org/elasticsearch/client/documentation
 
 include::../Versions.asciidoc[]