Fix stale comment in spec-test.js header after the module split

The header still said the suite loads js/statum.js; it loads
js/statum-core.js and js/statum-markdown.js in order now.

tests/markdown/spec-test.js

@@ -1,7 +1,8 @@
 /**
  * CommonMark 0.31.2 spec conformance runner.
  *
- * Loads js/statum.js through the DOM shim, renders every example in
+ * Loads js/statum-core.js + js/statum-markdown.js through the DOM shim,
+ * renders every example in
  * spec-tests.json and compares (whitespace-normalised) against the expected
  * HTML. Sections listed in OUT_OF_SCOPE are counted separately: they cover
  * raw HTML pass-through and schemes we deliberately neutralise, so they are