checking a single file causes false positives

[kevgo]

Steps to reproduce:

• go to the Git Town codebase
• run tools/rta npm exec text-runner website/src/commands/append.md

Expected behavior:

• it verifies this file and finds no issues

Actual behavior:

• it complains about links to non-existing files that actually exist

Additional thoughts:

• it should parse all files, but then only check the given file