Fix host to 0.0.0.0 (#3099)

frameworks/Crystal/amber/config/application.cr

@@ -7,4 +7,5 @@ Amber::Server.configure do |app|
   app.name = "TFB test app"
   app.color = false
   app.port = 8080
+  app.host = "0.0.0.0"
 end