Bump minimum node version.

[wtgtybhertgeghgtwtg]

If you bump the minimum node version to at least 4.0.0, you can drop the dependency on os-tmpdir. I can write a PR for this if you would like.

[silkentrance]

I for myself would be glad to drop support for node versions older than 4.0.0. However, I do not know if there are people out there still using it with node versions <4.0.0. Perhaps @raszi can direct us.

In any way, getting rid of older node versions is definitely worth a major version bump, say 1.0.0? #75

[wtgtybhertgeghgtwtg]

Support for node<4.0.0 has been dropped. Will this be considered?

[silkentrance]

minimum node version has been bumped to >=0.10.0

[silkentrance]

Dropping support for node versions < 4.0.0 allows us to use os.tmpdir().

Deprecated: This is not needed anymore. require('os').tmpdir() in Node.js 4 and up is good.

[silkentrance]

Currently, we only build for and test against node >=6.

[silkentrance]

Since we no longer support node <6, I am closing this as done.