* 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
v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(mate::StringToV8(isolate, "Menu"));
  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .MakeDestroyable()
      .SetMethod("insertItem", &Menu::InsertItemAt)
      .SetMethod("insertCheckItem", &Menu::InsertCheckItemAt)
      .SetMethod("insertRadioItem", &Menu::InsertRadioItemAt)
      .SetMethod("insertSeparator", &Menu::InsertSeparatorAt)
      .SetMethod("insertSubMenu", &Menu::InsertSubMenuAt)
      .SetMethod("setIcon", &Menu::SetIcon)
      .SetMethod("setSublabel", &Menu::SetSublabel)
      .SetMethod("setRole", &Menu::SetRole)
      .SetMethod("clear", &Menu::Clear)
      .SetMethod("getIndexOfCommandId", &Menu::GetIndexOfCommandId)
      .SetMethod("getItemCount", &Menu::GetItemCount)
      .SetMethod("getCommandIdAt", &Menu::GetCommandIdAt)
      .SetMethod("getLabelAt", &Menu::GetLabelAt)
      .SetMethod("getSublabelAt", &Menu::GetSublabelAt)
      .SetMethod("isItemCheckedAt", &Menu::IsItemCheckedAt)
      .SetMethod("isEnabledAt", &Menu::IsEnabledAt)
      .SetMethod("isVisibleAt", &Menu::IsVisibleAt)
      .SetMethod("popupAt", &Menu::PopupAt)
      .SetMethod("closePopupAt", &Menu::ClosePopupAt);
}
}  
}  
namespace {
using atom::api::Menu;
void Initialize(v8::Local<v8::Object> exports,