Update comment about `font-size` override for HTML element in PDF.js

The issue has been fixed upstream, but we need to keep the workaround
for old versions of PDF.js with Hypothesis embedded, that still exist on
various websites.

src/styles/annotator/pdfjs-overrides.scss

@@ -4,10 +4,9 @@
   display: none;
 }
 
-// Override PDFjs base font-size of miniscule `10px` to reset REM size.
-// This is necessary for styling components in shadow DOMs that rely on REM-
-// based scales.
-// See https://github.com/mozilla/pdf.js/issues/14555
+// Override tiny base 10px font-size in older versions of PDF.js. This is
+// necessary for styling components in shadow DOMs that rely on REM- based
+// scales. See https://github.com/mozilla/pdf.js/issues/14555.
 html {
   font-size: 100%;
 }