howto/tls: fix typo, specify actual fastly domain

howto/tls.md

@@ -265,8 +265,8 @@ time of writing (2020-04-15):
 
  * [Let's Encrypt][]: automatically issues certificates for most websites
    and domains, managed by TPA
- * [Globalsign][]: used by the [Fastly][] CDN used to distributed
-   TBB updates
+ * [Globalsign][]: used by the [Fastly][] CDN used to distribute
+   TBB updates (`cdn-fastly.torproject.org`)
  * [Digicert][]: used by other teams to sign software releases for
    Windows
  * [Harica][]: used for HTTPS on the donate.tpo onion service