Update changelog and version for v6.3.4.

Author: lgarron

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 6.3.4
+
+- CSP: Do not deduplicate alternate schema source expressions (@keithamus): https://github.com/github/secure_headers/pull/478
+
 ## 6.3.3
 
 Fix hash generation for indented helper methods (@rahearn)

lib/secure_headers/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module SecureHeaders
-  VERSION = "6.3.3"
+  VERSION = "6.3.4"
 end