Fix compatibility issue with sysinfo 0.31.0

virtweb_backend/src/controllers/server_controller.rs

@@ -171,7 +171,7 @@ pub async fn network_hook_status() -> HttpResult {
 
 pub async fn number_vcpus() -> HttpResult {
     let mut system = System::new();
-    system.refresh_cpu();
+    system.refresh_cpu_all();
     let number_cpus = system.cpus().len();
     assert_ne!(number_cpus, 0, "Got invlid number of CPU!");