Fail if metadata.json has no proper newline

[bastelfreak]

Should be rebased after #152 is merged.

Since ages, it's in our style guide that files need to end with a newline (https://voxpupuli.org/docs/reviewing_pr/), also the FHS demands it.

[ekohl]

Thinking out loud: is there a chance someone runs this interactively and passes it in via stdin? It may be too much of an edge case to care about, but users may do echo '{}' | metadata-json-lint /dev/stdin to only verify the schema. I can see editors with language servers apply this technique.

[bastelfreak]

echo '{}' | metadata-json-lint /dev/stdin works with this branch and on the master branch

$ echo '{}' | bundle exec metadata-json-lint /dev/stdin
(ERROR) required_fields: The file did not contain a required property of 'author'
(ERROR) required_fields: The file did not contain a required property of 'dependencies'
(ERROR) required_fields: The file did not contain a required property of 'license'
(ERROR) required_fields: The file did not contain a required property of 'name'
(ERROR) required_fields: The file did not contain a required property of 'source'
(ERROR) required_fields: The file did not contain a required property of 'summary'
(ERROR) required_fields: The file did not contain a required property of 'version'
Errors found in /dev/stdin

[ekohl]

echo '{}' | metadata-json-lint /dev/stdin works with this branch and on the master branch

That surprises me. I'd have expected that to fail on a missing newline. Now that I think about it, echo adds that. So a way to force this failure is echo -n '{}' | metadata-json-lint /dev/stdin