Use modern command name for electron-builder
Use modern command name for electron-builder

`electron-builder` now recommends you invoke it via that name instead of `build`
as was previously supported.

vector-im/vector-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web