Update build file due to doc file rename

A file with uncoverted snippets was change as part of 7f47ff9, but
build.gradle was not updated to reflect the rename.

x-pack/docs/build.gradle

@@ -81,7 +81,7 @@ buildRestTests.expectedUnconvertedCandidates = [
         'en/rest-api/ml/validate-job.asciidoc',
         'en/rest-api/security/authenticate.asciidoc',
         'en/rest-api/watcher/stats.asciidoc',
-        'en/security/authorization.asciidoc',
+        'en/security/authorization/overview.asciidoc',
         'en/watcher/example-watches/watching-time-series-data.asciidoc',
 ]