[feat] Support extra charset info in Content-Type header (#619)

XHR Polling failed to make handshake with server that adds charset info into Content-Type header.

Closes #618

lib/transports/polling-xhr.js

@@ -245,7 +245,7 @@ Request.prototype.create = function () {
         if (xhr.readyState === 2) {
           try {
             var contentType = xhr.getResponseHeader('Content-Type');
-            if (self.supportsBinary && contentType === 'application/octet-stream') {
+            if (self.supportsBinary && contentType === 'application/octet-stream' || contentType === 'application/octet-stream; charset=UTF-8') {
               xhr.responseType = 'arraybuffer';
             }
           } catch (e) {}
@@ -357,7 +357,7 @@ Request.prototype.onLoad = function () {
     try {
       contentType = this.xhr.getResponseHeader('Content-Type');
     } catch (e) {}
-    if (contentType === 'application/octet-stream') {
+    if (contentType === 'application/octet-stream' || contentType === 'application/octet-stream; charset=UTF-8') {
       data = this.xhr.response || this.xhr.responseText;
     } else {
       data = this.xhr.responseText;