[fix] Set accept header to */* to support react app proxy (#508)

Author: Tom Atkinson

lib/transports/polling-xhr.js

@@ -219,6 +219,10 @@ Request.prototype.create = function () {
       } catch (e) {}
     }
 
+    try {
+      xhr.setRequestHeader('Accept', '*/*');
+    } catch (e) {}
+
     // ie6 check
     if ('withCredentials' in xhr) {
       xhr.withCredentials = true;