7.1.1-7.1.2 seems to break coverage reporting on macos/ubuntu/windows with Node 10 (only)

• Version: 7.1.2
• Platform: ubuntu-latest/Node 10

https://github.com/DavidAnson/markdownlint runs c8 against master every day. After 10 successful runs with no changes to that branch, it started failing yesterday: https://github.com/DavidAnson/markdownlint/actions?query=workflow%3ACI

I created a fork of master with c8 locked to 7.1.1: https://github.com/DavidAnson/markdownlint/tree/c8711

It passes: https://github.com/DavidAnson/markdownlint/actions/runs/98587182

I created a fork of master with c8 locked to 7.1.2: https://github.com/DavidAnson/markdownlint/tree/c8712

It fails: https://github.com/DavidAnson/markdownlint/actions/runs/98587661

To be clear, that is the only difference between the branches:

pi@claw:~/markdownlint $ git diff c8711..c8712
diff --git a/package.json b/package.json
index 1edc8d0..d16356a 100644
--- a/package.json
+++ b/package.json
@@ -35,7 +35,7 @@
   "devDependencies": {
     "@types/node": "~13.11.1",
     "browserify": "~16.5.1",
-    "c8": "7.1.1",
+    "c8": "7.1.2",
     "cpy-cli": "~3.1.0",
     "eslint": "~6.8.0",
     "eslint-plugin-jsdoc": "~22.1.0",

GitHub aggressively terminates Actions with a failure, but this run demonstrates that the same 7.1.2 that fails on ubuntu-latest/Node 10 passes on ubuntu-latest/Node 14: https://github.com/DavidAnson/markdownlint/actions/runs/98145382

The relevant command is: c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 node test/markdownlint-test.js. In the failure case, it reports 4 lines uncovered: helpers.js | 99.4 | 96.35 | 100 | 99.4 | 156,194,197,554

The corresponding file: https://github.com/DavidAnson/markdownlint/blob/c8712/helpers/helpers.js

The first of the corresponding lines: https://github.com/DavidAnson/markdownlint/blob/34e2fd057648fda7559185e9aeaa68284f0d359b/helpers/helpers.js#L156

Please let me know if you need anything else from me.

[DavidAnson]

Just FYI, my thinking is to update the Workflow thusly:

- name: Run All Validations
  if: ${{ matrix.node-version != 10.x }}
  run: npm run ci
- name: Run Tests Only
  if: ${{ matrix.node-version == 10.x }}
  run: npm run test

[bcoe]

@DavidAnson I think it would be good to add a section to the README that covers this topic, it’s definitely confusing that the engine matters so much.