Fix 55

[jonasfj]

please double check golden files during review

---

Fixes #55.

When the value is empty the SourceSpan for the YamlNode representing
the value in a map points to the colon.

Example:

foo:
  bar:

The YamlNode for foo.bar has a value of null and starts and ends
at the colon : following bar. This means that removal might leave
the colon behind, which causes invalid YAML.

We have the same issue when removing foo.bar from the following YAML
document:

foo:
  baz: true
  bar:

However, in this case, we have a hack that ensures we always strip away
the any comments that follows bar. We do this by deleting up-to the
next newline. If we apply the same hack when removing foo.bar in the
first example, then it works.

One could argue that it works by accident, but it's kind of desired that
trailing comments are removed, when the value they are trailing is
removed.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:yaml_edit	2.2.1	ready to publish	v2.2.1

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[sigurdm]

Side-note - we should probably cache the result of getLineEnding somewhere.
Not in this PR.

[jonasfj]

yeah, some of this could benefit from more structure.
But performance isn't really much of a concern.