Bump webpush from 0.3.7 to 0.3.8 (#10592)

Bumps [webpush](https://github.com/zaru/webpush) from 0.3.7 to 0.3.8.
- [Release notes](https://github.com/zaru/webpush/releases)
- [Changelog](https://github.com/zaru/webpush/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zaru/webpush/compare/v0.3.7...v0.3.8)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -640,7 +640,7 @@ GEM
       activesupport (>= 4.2)
       rack-proxy (>= 0.6.1)
       railties (>= 4.2)
-    webpush (0.3.7)
+    webpush (0.3.8)
       hkdf (~> 0.2)
       jwt (~> 2.0)
     websocket-driver (0.7.0)