Certificate file name extensions unified (#354)

* Fix for default smtp certificate name

This fixes the defaut smtp certificate file name from smtp.crt to smtp.cert as it is used throughout the postal code.

script/install/ubuntu1604.sh

@@ -67,7 +67,7 @@ postal start
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 cp /opt/postal/app/resource/nginx.cfg /etc/nginx/sites-available/default
 mkdir /etc/nginx/ssl/
-openssl req -x509 -newkey rsa:4096 -keyout /etc/nginx/ssl/postal.key -out /etc/nginx/ssl/postal.crt -days 365 -nodes -subj "/C=GB/ST=Example/L=Example/O=Example/CN=example.com"
+openssl req -x509 -newkey rsa:4096 -keyout /etc/nginx/ssl/postal.key -out /etc/nginx/ssl/postal.cert -days 365 -nodes -subj "/C=GB/ST=Example/L=Example/O=Example/CN=example.com"
 service nginx reload
 
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