fix(config): correct typo in tempate ("is on" -> "the")

Author: Flottegurke

.env.template

@@ -611,7 +611,7 @@
 # SMTP_AUTH_MECHANISM=
 
 ## Server name sent during the SMTP HELO
-## By default this value should be is on the machine's hostname,
+## By default this value should be the machine's hostname,
 ## but might need to be changed in case it trips some anti-spam filters
 # HELO_NAME=