refactor: adjust tsconfig

[tobiasengelhardt]

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/CirclonGroup/angular-tree-component/blob/master/CONTRIBUTING.md#commit-message-guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

tsconfig still had an old reference to the file structure before the new lib structure. This caused some code editors to not pick up the tsconfig correctly and highlight wrong things in the angular-tree-component lib folder.

What is the new behavior?

Removed old reference.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information