partial fix for #107, set application/json to be default content-type

lib/swagger.js

@@ -1191,7 +1191,7 @@ var SwaggerRequest = function(type, url, params, opts, successCallback, errorCal
 SwaggerRequest.prototype.setHeaders = function(params, operation) {
   // default type
   var accepts = "application/json";
-  var consumes = null;
+  var consumes = "application/json";
 
   var allDefinedParams = this.operation.parameters;
   var definedFormParams = [];