Bump secure_headers from 6.1.2 to 6.3.0

Bumps [secure_headers](https://github.com/twitter/secureheaders) from 6.1.2 to 6.3.0.
- [Release notes](https://github.com/twitter/secureheaders/releases)
- [Changelog](https://github.com/twitter/secure_headers/blob/master/CHANGELOG.md)
- [Commits](github/secure_headers@v6.1.2...v6.3.0)

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

Gemfile.lock

@@ -417,7 +417,7 @@ GEM
       sprockets (> 3.0)
       sprockets-rails
       tilt
-    secure_headers (6.1.2)
+    secure_headers (6.3.0)
     selenium-webdriver (3.142.7)
       childprocess (>= 0.5, < 4.0)
       rubyzip (>= 1.2.2)