Fix: missing custom port on re-written links

When a link was rewritten and the site is running in a custom
(ie, not protocol standard - http/80, https/443) port, the links
became invalid.

We now include them only when necessary.

src/wikiless.js

@@ -48,8 +48,10 @@ if(config.https_enabled) {
   }
   https = require('https').Server(credentials, app)
   global.protocol = 'https://'
+  global.custom_port = config.ssl_port === '443' ? '' : `:${config.ssl_port}`
 } else {
   global.protocol = 'http://'
+  global.custom_port = config.nonssl_port === '80' ? '' : `:${config.nonssl_port}`
 }
 
 const http = require('http').Server(app)