RC 8 - Bug fixes, automatic testing with Jest

Features:

• If your project uses Jest, you will be prompted to set up a Spectron test when adding this plugin (#128, 57895c7)

Bug fixes:

• The app protocol is used to load index.html, fixes some CORS issues (#129, 8dc5bba)
• --dashboard is now removed from electron-builder args, so builds started with the CLI UI will work (#48 (comment), d122fe6)