[Cleanup] Fix broken link in feature_policy.h

This CL updates a broken feature policy spec link.

Change-Id: I1b17e473fa9ce146a97a44ef78a8d2ce1e7fb2a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490264Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Charlie Hu <chenleihu@google.com>
Cr-Commit-Position: refs/heads/master@{#819482}

third_party/blink/public/common/feature_policy/feature_policy.h

@@ -28,7 +28,7 @@ namespace blink {
 // HTTP header, or can be set by the |allow| attributes on the iframe element
 // which embeds the document.
 //
-// See https://wicg.github.io/FeaturePolicy/
+// See https://w3c.github.io/webappsec-permissions-policy/
 //
 // Key concepts:
 //