fix type hint errors

[xinningsu]

fopen 返回值不是 string, 是 resource
不过type hint中并没有resource这个类型，看官方接口也没有定义返回类型，所以直接去掉

#22 {main} {"memory":4070200,"exception":"[object] (TypeError(code: 0): Overtrue\\Flysystem\\Qiniu\\QiniuAdapter::readStream(): Return value must be of type string, resource returned at /Users/thomas/projects/craft-4/vendor/overtrue/flysystem-qiniu/src/QiniuAdapter.php:95)"} 

另外修复了测试函数也有两处type hint问题

1) Overtrue\Flysystem\Qiniu\Tests\QiniuAdapterTest::testGetUploadToken with data set #0 (Mockery_0_Overtrue_Flysystem_Qiniu_QiniuAdapter Object (...), array(Mockery_1_stdClass Object (...), Mockery_1_stdClass Object (...), Mockery_1_stdClass Object (...), Mockery_1_stdClass Object (...)))
TypeError: Mockery_0_Overtrue_Flysystem_Qiniu_QiniuAdapter::getUploadToken(): Argument #3 ($policy) must be of type ?array, string given, called in /Users/thomas/projects/flysystem-qiniu/tests/QiniuAdapterTest.php on line 312