Fix vector config performance suggestion (#1115)

Author: JPryce-Aklundh

modules/ROOT/pages/indexes/semantic-indexes/vector-indexes.adoc

@@ -258,7 +258,7 @@ If you are using a compatible version of Java, you can add the following setting
 .Configuration settings
 [source,config]
 ----
-server.jvm.additional=--add-modules jdk.incubator.vector
+server.jvm.additional=--add-modules=jdk.incubator.vector
 ----
 
 [[show-vector-indexes]]