* Output of `node_modules/.bin/electron --version`: v3.0.6
* Operating System (Platform and Version): Windows 10 (October Update)

**Expected Behavior**
When using the accelerator "Shift+Backspace" in a `Menu`, the accelerator should be displayed as "Shift+Backspace"

**Actual behavior**
"Shift+Shift+Backspace" is displayed as accelerator in the menu.

**To Reproduce**
See: https://github.com/torjusb/electron-accelerator-bug

**Screenshots**
<img width="385" alt="accelerator" src="https://user-images.githubusercontent.com/53583/47494149-49635f80-d851-11e8-8178-eed38f22e0e2.png">

**Additional info**
This only appears to affect "Shift+Backspace" from limited testing. Accelerators such as "Alt+Backspace", "Shift+M" etc. appears to work fine.
atom/browser/api/atom_api_menu.cc
mate::Dictionary wrappable(isolate, GetWrapper());
  mate::Dictionary delegate;
  if (!wrappable.Get("delegate", &delegate))
    return;
  delegate.Get("isCommandIdChecked", &is_checked_);
  delegate.Get("isCommandIdEnabled", &is_enabled_);
  delegate.Get("isCommandIdVisible", &is_visible_);
  delegate.Get("getAcceleratorForCommandId", &get_accelerator_);
  delegate.Get("executeCommand", &execute_command_);
  delegate.Get("menuWillShow", &menu_will_show_);
}
bool Menu::IsCommandIdChecked(int command_id) const {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  return is_checked_.Run(GetWrapper(), command_id);
}
bool Menu::IsCommandIdEnabled(int command_id) const {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  return is_enabled_.Run(GetWrapper(), command_id);
}
bool Menu::IsCommandIdVisible(int command_id) const {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  return is_visible_.Run(GetWrapper(), command_id);
}
bool Menu::GetAcceleratorForCommandIdWithParams(