Update Travis to create builds

[matt-auckland]

Update Travis so that it builds out each platform

• Windows (Electron)
• OSX (Electron)
• Linux (Electron)
• Android (Cordova? Native Script?)
• iOS (Cordova? Native Script?)

Do we want to build all our languages at the moment? Not sure it's worth the overhead until we sort out a better solution. Otherwise we're going to be making number-of-platforms * number-of-languages build artefacts