fix typo in mailhog readme (#30)

Author: lukqw

mailhog/README.md

@@ -1,7 +1,7 @@
 LocalStack Mailhog Extension
 ===============================
 
-Web and API based STMP testing directly in LocalStack using [MailHog](https://github.com/mailhog/MailHog).
+Web and API based SMTP testing directly in LocalStack using [MailHog](https://github.com/mailhog/MailHog).
 
 If the standard configuration is used, LocalStack will serve the UI through http://mailhog.localhost.localstack.cloud:4566 or http://localhost:4566/mailhog/.
 It will also configure `SMTP_HOST` automatically, which points all services using SMTP, including [SES](https://docs.localstack.cloud/user-guide/aws/ses/), to MailHog.