Inconsistent exit code when invalid files is more than 255

[dmromanov]

Exit code does not match count of invalid files if there are more than 255 erroneous files.

Exit code should not exceed 127 on most platforms.
See https://en.wikipedia.org/wiki/Exit_status

It's better to have a fixed error exit code.

jsonlint-tree/index.js

Line 36 in 5d4a522

process.exit(failed)