content/static/doc: fix typo in 'go mod why' reference

For golang/go#33637

Change-Id: Iba37b9ea0024e5c07d14d57861b4705d29f59e44
Reviewed-on: https://go-review.googlesource.com/c/website/+/285432
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

content/static/doc/mod.md

@@ -1635,7 +1635,7 @@ command line, separated by blank lines. Each stanza begins with a comment line
 starting with `#` giving the target package or module. Subsequent lines give a
 path through the import graph, one package per line. If the package or module
 is not referenced from the main module, the stanza will display a single
-parenthesized not indicating that fact.
+parenthesized note indicating that fact.
 
 For example: