Fix email redirect format in _redirects file (#2286)

Updated email redirect to include a forward slash before the splat.

Author: abovedave

packages/stacks-docs/_redirects

@@ -2,9 +2,8 @@
 https://alpha.stackoverflow.design/*             https://stackoverflow.design/:splat            301
 https://beta.stackoverflow.design/*              https://stackoverflow.design/:splat            302
 
-
 # Email section → v2 docs
-/email/*                                         https://v2.stackoverflow.design/email:splat     302
+/email/*                                         https://v2.stackoverflow.design/email/:splat   302
 
 # Redirects from v2 urls
 /product                                        /system/develop/using-stacks/                   302