rubygem-paperclip -- validation bypass vulnerability

Jon Yurek reports:

Thanks to MORI Shingo of DeNA Co., Ltd. for reporting this.
There is an issue where if an HTML file is uploaded with a .html
extension, but the content type is listed as being image/jpeg,
this will bypass a validation checking for images. But it will also
pass the spoof check, because a file named .html and containing
actual HTML passes the spoof check.
This change makes it so that we also check the supplied content
type. So even if the file contains HTML and ends with .html, it
doesn’t match the content type of image/jpeg and so it fails.