updated lib to address content types

lib/swagger-client.js

@@ -2173,8 +2173,8 @@ Operation.prototype.execute = function(arg1, arg2, arg3, arg4, parent) {
     fail(message);
     return;
   }
-
   var headers = this.getHeaderParams(args);
+  headers = this.setContentTypes(args, opts);
   var body = this.getBody(headers, args);
   var url = this.urlify(args);