fix: only match zero or one occurrence of .cn suffix

aws4.js

@@ -57,7 +57,7 @@ function RequestSigner(request, credentials) {
 }
 
 RequestSigner.prototype.matchHost = function(host) {
-  var match = (host || '').match(/([^\.]+)\.(?:([^\.]*)\.)?amazonaws\.com(\.cn)*$/)
+  var match = (host || '').match(/([^\.]+)\.(?:([^\.]*)\.)?amazonaws\.com(\.cn)?$/)
   var hostParts = (match || []).slice(1, 3)
 
   // ES's hostParts are sometimes the other way round, if the value that is expected