ci: appveyor builds are trying to get electron arm builds for windows

[kewde]

The AppVeyor builds for electron 5.0.0 and 6.0.0 are not completing because they are unable to retrieve the ARM bins. Even though we have no ARM supported prebuilts, the failing of the download still blocks the process.

[kewde]

Blocked until a new release of node-gyp nodejs/node-gyp#1934

[kewde]

Tracking release here nodejs/node-gyp#1935

[kewde]

#1245