Issue Summary

When we export blog using ghost-cli ghost export, we can name it using any filename and extension. But when we import it into the other ghost server using ghost-cli ghost import, if we use the file which is not a JSON extension (.json) the cli vaidation will thow an error.

Expected

it shouldn't validate using file extension and using JSON (content) validation instead.
So any file name without .json but contain the JSON content should've worked as well.

✖ Running blog import
An error occurred.
Message: 'Response code 415 (Unsupported Media Type)'

To Reproduce

1. ghost export testimportfile
2. ghost import testimportfile

Technical details:

Debug Information:
OS: Ubuntu, v18.04.4 LTS
Node Version: v10.19.0
Ghost Version: 3.11.0
Ghost-CLI Version: 1.13.1
Environment: production
Command: 'ghost import bckfile'