Description:
------------
Using the following JSON document:

{
    "foo": []
}

finfo::file method wrongly returns text/plain as mime type instead of application/json.

Modifying the JSON document to e.g.:

{
    "foo": ["bar"]
}

makes the function behave correctly and returns application/json.

Test script:
---------------
<?php

$finfo = new finfo(FILEINFO_MIME_TYPE);

echo $finfo->file('file.json') . PHP_EOL;


Expected result:
----------------
With the following content of file.json:

{
    "foo": []
}

I expect to see "application/json" as the output.

Actual result:
--------------
With the following content of file.json:

{
    "foo": []
}

"text/plain" is returned.