* 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
int command_id,
                             const base::string16& label) {
  model_->InsertCheckItemAt(index, command_id, label);
}
void Menu::InsertRadioItemAt(int index,
                             int command_id,
                             const base::string16& label,
                             int group_id) {
  model_->InsertRadioItemAt(index, command_id, label, group_id);
}
void Menu::InsertSubMenuAt(int index,
                           int command_id,
                           const base::string16& label,
                           Menu* menu) {
  menu->parent_ = this;
  model_->InsertSubMenuAt(index, command_id, label, menu->model_.get());
}
void Menu::SetIcon(int index, const gfx::Image& image) {
  model_->SetIcon(index, image);
}
void Menu::SetSublabel(int index, const base::string16& sublabel) {
  model_->SetSublabel(index, sublabel);
}
void Menu::SetRole(int index, const base::string16& role) {
  model_->SetRole(index, role);
}
void Menu::Clear() {
  model_->Clear();
}
int Menu::GetIndexOfCommandId(int command_id) {