Add support for electron `v29` prebuilds

[m4heshd]

Stable electron v29 just released. Prebuilds were tested here but the tests are failing with the following error.

D:\better-sqlite3\build\src\util\macros.lzz(150,33): error C2664: 'void v8::ObjectTemplate::SetAccessor(v8::Local<v8::String>,v8::AccessorGetterCallback,v8::AccessorSetterCallback,
v8::Local<v8::Value>,v8::PropertyAttribute,v8::SideEffectType,v8::SideEffectType)': cannot convert argument 5 from 'v8::AccessControl' to 'v8::PropertyAttribute' [D:\better-sqlite3\build\better_sqlite3.vcxproj]

Pinging @JoshuaWise.