Update upgrading-to-3-0.md

Author: oreoshake

upgrading-to-3-0.md

@@ -8,6 +8,7 @@ Changes
 | Global configuration             | `SecureHeaders::Configuration.configure` block             | `SecureHeaders::Configuration.default` block                                                                                                                                 |
 | All headers besides HPKP and CSP | Accept hashes as config values                           | Must be strings (validated during configuration)                                                                                                                                                            |
 | CSP directive values             | Accepted space delimited strings OR arrays of strings    | Must be arrays of strings                                                                                                                                                  |
+| CSP Nonce values in views             | `@content_security_policy_nonce`    | `content_security_policy_script_nonce` or `content_security_policy_style_nonce`
 | `self`/`none` source expressions     | could be `self` / `none` / `'self'` / `'none'`                   | Must be `'self'` or `'none'`                                                                                                                                                   |
 | `inline` / `eval` source expressions | could be `inline`, `eval`, `'unsafe-inline'`, or `'unsafe-eval'` | Must be `'unsafe-eval'` or `'unsafe-inline'`                                                                                                                                   |
 | Per-action configuration         | override [`def secure_header_options_for(header, options)`](https://github.com/twitter/secureheaders/commit/bb9ebc6c12a677aad29af8e0f08ffd1def56efec#diff-04c6e90faac2675aa89e2176d2eec7d8R111)  | Use [named overrides](https://github.com/twitter/secureheaders#named-overrides) or [per-action helpers](https://github.com/twitter/secureheaders#per-action-configuration) |