Fix futured_on typo

Key is 'future_on'

Change-Id: Ibef7b85ea6fa4853effb922b1d9d0383ec536e30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300005Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Chris Sharp <csharp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791832}

components/policy/resources/policy_templates.json

@@ -108,7 +108,7 @@
 #   |since_version| and is removed after |until_version|. |until_version|
 #   is optional.
 #
-#   The format of the 'futured_on' list entries is '<platform>'.
+#   The format of the 'future_on' list entries is '<platform>'.
 #   There is no version range attached to it and the policy is available in the
 #   Dev and Canary channel only unless it's listed in the
 #   EnableExperimentalPolicies policy.