修改 post demo

Author: carsonxu

demo/sts-form.html

@@ -16,6 +16,7 @@ <h1>Form 表单简单上传（兼容 IE8）</h1>
     <input id="success_action_redirect" name="success_action_redirect" type="hidden" value="">
     <input id="key" name="key" type="hidden" value="">
     <input id="Signature" name="Signature" type="hidden" value="">
+    <input name="Content-Type" type="hidden" value="">
     <input id="x-cos-security-token" name="x-cos-security-token" type="hidden" value="">
     <input id="fileSelector" name="file" type="file">
     <input id="submitBtn" type="button" value="提交">

demo/sts-post.html

@@ -69,6 +69,7 @@ <h1>Ajax Post 上传</h1>
                 var fd = new FormData();
                 fd.append('key', Key);
                 fd.append('Signature', auth);
+                fd.append('Content-Type', '');
                 XCosSecurityToken && fd.append('x-cos-security-token', XCosSecurityToken);
                 fd.append('file', file);
                 var url = prefix;