deps: upgrade npm to 2.6.1

[othiym23]

This is a comparatively modest update, at least compared to npm@2.7.0, which includes at least one feature that is very relevant to io.js's interests (foreshadowing!). Here are the pertinent changes in npm@2.6.1:

• 8b98f0e
  #4471 npm outdated (and only npm outdated) now defaults to --depth=0. This also has the excellent but unexpected effect of making npm update -g work the way almost everyone wants it to. See the docs for
  --depth
  for the mildly confusing details. (@smikes)
• aa79194
  #6565 Tweak peerDependency
  deprecation warning to include which peer dependency on which package is
  going to need to change. (@othiym23)
• 5fa067f
  #7171 Tweak engineStrict
  deprecation warning to include which package.json is using it.
  (@othiym23)

@bnoordhuis, do the floating patches for node-gyp still need to be applied, or did da730c7 take care of one or both of them? I was unclear on this, so held off on applying them.

[cjihrig]

da730c7 partially reverted one of the floating patches. I think that means there are now 3 :-/

[othiym23]

@cjihrig That's fine – if somebody can provide me a list of SHAs, I'm happy to cherry-pick them onto the PR and verify that the npm build still works.

[Fishrock123]

Can't we just squash the patches down and link to the originals?

[othiym23]

What I would prefer is to get a new version of node-gyp out so that we can fix this issue permanently. ;) As long as that's not an option, I am entirely in favor of whatever works. Cherry-picking the patches as individual commits takes barely any time at all, because they all apply cleanly over the top of deps/npm.

[cjihrig]

I agree that fixing the problem in node-gyp would be most ideal. I also like @Fishrock123's idea of squashing the commits in the mean time. The original commits are in #343, #422, and #918. I also have a squashed version of those three commits in https://github.com/cjihrig/io.js/commit/723a2d14a62635ae15b487e6de4c6a3e5db1fc00, which you are welcome to use if no one is opposed.

[Fishrock123]

@cjihrig may be nice / better to link to the original commits, rather than the PR's. :)

[cjihrig]

The commits themselves have appeared in the history multiple times, that's why I linked to the PRs. The original commits are 03d1992, 5de334c, and da730c7

[bnoordhuis]

@cjihrig Can I suggest you link to the original commits in the commit log? Apart from that LGTM if installing and building still works. Land at will.

[cjihrig]

Thanks! Landed in 2a2fe5c, with the floating patches applied in 58a612e.

[othiym23]

🎉