Add Flatpak and snap to Step::System (#218)

This makes them easier to disable

src/main.rs

@@ -396,6 +396,7 @@ fn run() -> Result<(), Error> {
 
     #[cfg(target_os = "linux")]
     {
+        if config.should_run(Step::System) {
             execute(
                 &mut report,
                 "Flatpak",
@@ -409,6 +410,7 @@ fn run() -> Result<(), Error> {
                 config.no_retry(),
             )?;
         }
+    }
 
     if let Some(commands) = config.commands() {
         for (name, command) in commands {