Fix bug when reading environment variables

src/configuration.rs

@@ -18,7 +18,7 @@ pub fn get_configuration() -> Result<Settings, config::ConfigError> {
         .add_source(
             config::Environment::with_prefix("APP")
                 .prefix_separator("_")
-                .prefix("__"),
+                .separator("__"),
         )
         .build()?;