Fix default branch name in comment

Author: chalin

netlify.toml

@@ -1,6 +1,6 @@
 [build]
 # This default build command adds the robots noindex directive to the site headers.
-# It is turned off for only for the production site by using [context.master] below
+# It is turned off for only for the production site by using [context.main] below
 # DO NOT REMOVE THIS (contact @kubernetes/sig-docs-leads)
 publish = "public"
 functions = "functions"