Improvement: Build with LTS version of Node and AppVeyor

[hypery2k]

The current travis configuration uses Node 7 to build. It would be better to stick to Node 8 or the upcoming NodeLTS version, see here for more.
Node 8 also improves overall install performance an dev machine. Maybe it would be also a good idea to test several NodeJS version, like here.
Besides that a ci build on AppVeyor would also ensure that the setup works on Windows machines.

I could sent a PR for these both issue.

[subsend]

Hey, thanks for Idea! 384575c

[Waschnick]

@subsend upgraded to a newer node version with his commit (he forgot the PR and to mention the issue in the commit ;) )

AppVeyor may be a good idea, for testing windows, as I have a Windows machine at home ;) @hypery2k feel free to create a PR for the pull request

As for multiple node versions - what would be the benefit?

[hypery2k]

the multiple node version would just help in case for development. Sometimes dependencies and build stuff works differently in different version, so for a library on the use side no big issue