fix: yarn-lock-v2 parsing with absent dependencies field in package.json

[tarik02]

• [x] Tests written and linted
• [ ] Documentation written / README.md updated https://snyk.io/docs/snyk-for-node/
• [x] Follows CONTRIBUTING agreement
• [x] Commit history is tidy https://git-scm.com/book/en/v2/Git-Branching-Rebasing
• [ ] Reviewed by Snyk team

What this does

Explain why this PR exists To fix bug explained in #276

Notes for the reviewer

More information

• #276

Screenshots