small doc fix for updates related to _source defaults found by community member (elastic#118605) (elastic#118611)

Author: john-wagster

docs/reference/docs/update.asciidoc

@@ -71,7 +71,7 @@ include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=refresh]
 include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=routing]
 
 `_source`::
-(Optional, list) Set to `false` to disable source retrieval (default: `true`).
+(Optional, list) Set to `true` to enable source retrieval (default: `false`).
 You can also specify a comma-separated list of the fields you want to retrieve.
 
 `_source_excludes`::