Very oddly, there seems to be no way of setting Google Document links to open in a new window. (target=\"_blank\").
When publishing a Google Doc and using the embed
A simpler, non-coding workaround is to embed the google document from Google Drive, instead of the 'published' google doc. Permissions can allow you to ensure document viewership and circulation is restricted.
Follow this link and see the section under 'Google Drive'
This worked perfectly for us - links are opening without a warning that can frighten users.