Fix service file for execution

files/hedgedocs.service

@@ -14,7 +14,7 @@ Type=exec
 Environment=NODE_ENV=production
 Restart=always
 RestartSec=2s
-ExecStart=/usr/bin/yarn start --production
+ExecStart=npm start --production
 CapabilityBoundingSet=
 NoNewPrivileges=true
 PrivateDevices=true
@@ -39,7 +39,7 @@ SystemCallFilter=@system-service
 
 # You may have to adjust these settings
 User=hedgedocs
-Group=hedgedocs
+Group=wwww-data
 WorkingDirectory=/home/hedgedocs/hedgedoc
 
 # Example: local storage for uploads and SQLite