Make final new line optional

[simonnilsson]

Why am I submitting this PR

A new line is always added at end of output files. Depending on auto-formatting behavior of editor e.t.c. this might not always be desirable.

Does it fix an existing ticket?

No

Checklist

• [x] only relevant code is changed (make a diff before you submit the PR)
• [x] tests are included and pass: yarn test (see details here)
• [x] documentation is changed or added

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.36%. Comparing base (7e14d85) to head (910d3cc). Report is 44 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1014 +/- ## ========================================== + Coverage 95.16% 95.36% +0.20% ========================================== Files 11 10 -1 Lines 1922 1919 -3 ========================================== + Hits 1829 1830 +1 + Misses 93 89 -4 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.