bump dependencies, require node 4, remove home-path dependency

[develar]

electron-builder, electron-packager and electron-osx-sign required node 4, so, we can

• reduce number of dependencies and use os.homedir(),
• use babel preset es2015-node4.

Also, dependencies updated — fs-extra updated to 1.0.0.

path-exists updated to 3.0.0 — node <4 support is dropped (sindresorhus/path-exists#4).

[malept]

I already tried that once (see #30). We can't drop Node < 4.0 support until 2017, because electron-prebuilt depends on electron-download, and Node 0.12 is officially supported until the end of 2016. My plan was to remove babel from electron-download (and upgrade path-exists) after January 1.

[mafintosh]

There is a big difference between this module and the signing stuff. This one is used when people install electron (for example when people use https://github.com/mappum/electron-webrtc in node apps). I don't see the need to drop support for any node unless we really have to.

[malept]

I think it's reasonable to drop any Node version that the NodeJS team no longer maintains.

[wtgtybhertgeghgtwtg]

One argument for dropping support for older versions is that it would allow electron-download to use newer dependencies. For example, you could replace nugget or request with got and significantly reduce the dependency tree.

[develar]

@wtgtybhertgeghgtwtg it is what should be done, but nugget also provides progress bar — got doesn't provide this functionality. Task is not so easy.

[wtgtybhertgeghgtwtg]

If you can get nugget to bump their minimum required node version to at least 4, it can be changed to use got over request.

[develar]

@malept Conflicts resolved. Today is 1 Feb 2017 — time to remove < node 4 support :)