Fixed bugs reported by @encomer on Slack. Thanks!

dollar.rkt

@@ -26,7 +26,9 @@
          $$-mathjax
          use-katex
          use-mathjax
-         with-html5)
+         with-html5
+         use-external-katex
+         use-external-mathjax)
 
 (define-syntax (if-version≥6.12 stx)
   (syntax-case stx ()

scribblings/scribble-math.scrbl

@@ -250,7 +250,7 @@ details see the documentation of @racket[with-html5].
 
 @defproc[(use-tex2svg) void?]{
  This shorthand calls @racket[($-html-handler $-tex2svg)] and
- @racket[($$-html-handler $$-tex2svg)]. The mathematical forumulas passed to
+ @racket[($$-html-handler $$-tex2svg)]. The mathematical formulas passed to
  @racket[$] and @racket[$$] which appear later in the document will therefore be
  typeset using @tt{tex2svg}.