`ftd` should allow `jpeg` image format

[gsalunke]

while build if any image with jpeg image format is present in package throws below error:

Processing ftd.dev/journal.ftd ... Error: PackageError { message: "failed to parse ParseError { message: \"jpg is not present in ftd.dev/assets#file-record-images-ftd-language of type {\\\"jpeg\\\": Record { name: \\\"ftd#image-src\\\", default: None }, \\\"jpeg-page\\\": String { caption: false, body: false, default: None }}\", doc_id: \"ftd.dev/journal\", line_number: 2333 }" }