* 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
return model_->GetIndexOfCommandId(command_id);
}
int Menu::GetItemCount() const {
  return model_->GetItemCount();
}
int Menu::GetCommandIdAt(int index) const {
  return model_->GetCommandIdAt(index);
}
base::string16 Menu::GetLabelAt(int index) const {
  return model_->GetLabelAt(index);
}
base::string16 Menu::GetSublabelAt(int index) const {
  return model_->GetSublabelAt(index);
}
bool Menu::IsItemCheckedAt(int index) const {
  return model_->IsItemCheckedAt(index);
}
bool Menu::IsEnabledAt(int index) const {
  return model_->IsEnabledAt(index);
}
bool Menu::IsVisibleAt(int index) const {
  return model_->IsVisibleAt(index);
}
void Menu::OnMenuWillClose() {
  Emit("menu-will-close");
}
void Menu::OnMenuWillShow() {
  Emit("menu-will-show");
}
void Menu::BuildPrototype(v8::Isolate* isolate,