Docs: ensure headings with digits appear

docs/api-output.md

@@ -374,9 +374,9 @@ await sharp('in.gif', { animated: true })
   .gif({ interFrameMaxError: 8 })
   .toFile('optim.gif');
 ```
-<a name="jp2"></a>
 
-## jp
+
+## jp2
 Use these JP2 options for output image.
 
 Requires libvips compiled with support for OpenJPEG.

docs/build.js

@@ -29,8 +29,8 @@ const jsdoc2md = require('jsdoc-to-markdown');
   });
 
   const cleanMarkdown = markdown
-    .replace(/(## [A-Za-z]+)[^\n]*/g, '$1') // simplify headings to match those of documentationjs, ensures existing URLs work
-    .replace(/<a name="[A-Za-z+]+"><\/a>/g, '') // remove anchors, let docute add these (at markdown to HTML render time)
+    .replace(/(## [A-Za-z0-9]+)[^\n]*/g, '$1') // simplify headings to match those of documentationjs, ensures existing URLs work
+    .replace(/<a name="[A-Za-z0-9+]+"><\/a>/g, '') // remove anchors, let docute add these (at markdown to HTML render time)
     .replace(/\*\*Kind\*\*: global[^\n]+/g, '') // remove all "global" Kind labels (requires JSDoc refactoring)
     .trim();