Add fallback for mime.lookup

[codenirvana]

PR Checklist:

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
  
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]
  

PR Description

Instead of returning the first available type, mime-types simply returns false, so fallback to application/octet-stream.