修复204时response的异常

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@bytedo/fetch",
-  "version": "1.1.0",
+  "version": "1.1.1",
   "description": "全新的ajax封装。分2个版本, 一个基于XMLHttpRequest, 一个基于window.fetch",
   "main": "dist/index.js",
   "directories": {

src/index.es7

@@ -276,7 +276,7 @@ class _Request {
       result.statusText = this.xhr.statusText || ERRORS[10500]
     }
 
-    result.body = this.xhr.response
+    result.body = result.status === 204 ? null : this.xhr.response
 
     this.__success__(isSucc, result)
   }