Upgrade serialport to latest stable

[beriberikix]

trafficstars

See related spark/particle-cli#390. I also noticed we're using a fork of node-serialport - do we know if we can move to the mainline version?

[suda]

We're using the fork because the serialport module didn't previously work well with Electron. We could try using the latest version and seeing if it's ok now.

[beriberikix]

Makes sense, thanks for the background. It looks like there are now separate, optimized builds specifically for Electron ✨