[BUG] Item:MimeType seems invalid

[AlexV525]

https://developer.android.com/media/platform/motion-photo-format#item_element

In the official doc of Motion Photo, there is only Mime attribute, not MimeType.

motion_photos/lib/src/constants.dart

Line 13 in f1ec3d3

static String ItemMimeType = 'Item:MimeType';

[ua741]

Thank you for pointing this issue.
Surprisingly, in our current samples, we have never encountered a case where we needed to look up this attribute, as most of the motion photo samples were detected in the previous steps.