How to set number of lines to vertical scroll using mouse?

Following code does not work:

  {
    "button" : "scroll_down",
    "modifiers" : ],
    "command" : "scroll_lines",
    "args" : { "amount" : 1.0 }
  },
  {
    "button" : "scroll_up",
    "modifiers" : ],
    "command" : "scroll_lines",
    "args" : { "amount": -1.0 }
  }
]

File: ~/.config/sublime-text-3/Packages/User/Default (Linux).sublime-keymap
SublimeText 3, build 3065