ClientModified marshal format

[chyroc]

2022/02/24 17:07:56 Error in call to API function "files/upload": HTTP header "Dropbox-API-Arg": client_modified: time data '2022-02-24T16:50:46.921728694+08:00' does not match format '%Y-%m-%dT%H:%M:%SZ'

should format as '%Y-%m-%dT%H:%M:%SZ'