fix: work with ipv4 instead of relying on ipv6's ipv4 fallback (#299)

As per the docs:
> In most operating systems, listening to the unspecified IPv6 address (::) may cause the net.Server to also listen on the unspecified IPv4 address (0.0.0.0).

It turns out "most operating systems" is not good enough.

This fixes it since the default is:
> If host is omitted, the server will accept connections on the unspecified IPv6 address (::) when IPv6 is available, or the unspecified IPv4 address (0.0.0.0) otherwise.

Author: aliscott

src/server.ts

@@ -2,7 +2,7 @@ import createApp from './app';
 import config from './config';
 
 createApp().then((app) => {
-  app.listen(config.port, '::', () => {
+  app.listen(config.port, () => {
     config.logger.info(`🚀  Server ready at http://0.0.0.0:${config.port}/`);
   });
 });