Newer versions of FTB App create a stub version.json in the instance
root with only a comment directing to .ftbapp/version.json. The old
logic would find this stub file first and fail to parse it, causing
modpacks to not be detected.
This fix checks .ftbapp/version.json first (newer location) before
falling back to the root version.json (older location).
Signed-off-by: Marco von Rosenberg <codingmarco@gmail.com>
