Fix typo

By URL: https://docs.bazel.build/versions/master/skylark/backward-compatibility.html
stanza "!-- Add new options here -->" visible.

RELNOTES:none
PiperOrigin-RevId: 210690341
diff --git a/site/docs/skylark/backward-compatibility.md b/site/docs/skylark/backward-compatibility.md
index a1143ae..57ee0b0 100644
--- a/site/docs/skylark/backward-compatibility.md
+++ b/site/docs/skylark/backward-compatibility.md
@@ -436,4 +436,4 @@
 *   Default: `false`
 
 
-!-- Add new options here -->
+<!-- Add new options here -->